"I wish you great happiness here," Bush said. "I never felt the loneliness some Presidents have described."
Bush warned of tough times and criticism Clinton may not feel is warranted. "I'm not a very good one to give advice; but just don't let the critics discourage you or push you off course."
RELATED: See George H.W. and Barbara Bush throughout their lives
Barbara and George H.W. Bush through the years
Barbara and George H.W. Bush through the years
George Bush is shown with wife Barbara in 1945. (AP Photo)
George Herbert Walker Bush poses with his wife Barbara during his campaign for Congress in the 1960's. Born 12 June 1924 in Milton, Massachussetts, George Bush Yale graduated with a degree in Economics in 1948, made a fortune drilling oil before entering politics in 1964. US Congressman from Texas (1966-1970), ambassador to the United nations (1971-1974), Special Envoy to China (1974-1975), Republican National Chairman (1975-1976), Central Intelligence Agency (CIA) director (1976-1977), vice president of the US (1981-1959) George Bush is eventually elected president of the US 08 November 1988 against Democratic nominee Michael Dukakis. AFP PHOTO/WHITE HOUSE (Photo credit should read /AFP/Getty Images)
FILE - In this 1964 file photo, George H.W. Bush sits on couch with his wife Barbara and their children. George W. Bush sits at right behind his mother. Behind couch are Neil and Jeb Bush. Sitting with parents are Dorothy and Marvin Bush. Again? Really? There are more than 300 million people in America, yet the same two families keep popping up when it comes to picking a president. The possibility of a Bush-Clinton matchup in 2016 is increasingly plausible. After months of hints and speculation, former Florida Gov. Jeb Bush last week said he's actively exploring a bid for the Republican nomination. And while Hillary Rodham Clinton hasn't revealed her intentions, she's seen as the odds-on favorite for the Democratic nomination. By Nancy Benac. ? (AP Photo, File)
Republican Senatorial candidate George Bush shows a victory sign as he and his wife Barbara stand in front of a vote machine November 3, 1964 in Houston,Tex., just before casting their ballot. The candidate waited an hour and a half in a long of votes that circled the Pilgrim Elementary School where the Bush's voted this morning. in Houston. (AP Photo).
George Herbert Walker Bush poses with his wife Barbara in Beijing in 1974. Born 12 June 1924 in Milton, Massachussetts, George Bush Yale graduated with a degree in Economics in 1948, made a fortune drilling oil before entering politics in 1964. US Congressman from Texas (1966-1970), ambassador to the United nations (1971-1974), Special Envoy to China (1974-1975), Republican National Chairman (1975-1976), Central Intelligence Agency (CIA) director (1976-1977), vice president of the US (1981-1959) George Bush is eventually elected president of the US 08 November 1988 against Democratic nominee Michael Dukakis. AFP PHOTO/WHITE HOUSE (Photo credit should read /AFP/Getty Images)
LANGLEY. -- JAN. 26: President Gerald R. Ford and Barbara Bush watch as Justice Potter Stewart swears in George H.W. Bush as the new Director of the CIA, at CIA HQ in Langley, Virginia, January 26, 1976. The outgoing Director William Colby is at the left in the background. (Photo by David Hume Kennerly/Getty Images)
373743 02: Republican Presidential candidate George Bush, wearing a t-shirt referencing his son George W. Bush, stands with his wife Barbara November 1978 in Texas, USA. Bush is campaigning for the presidential primary elections. (Photo by Dirck Halstead/Liaison)
373749 01: Republican Presidential candidate George Bush looks at his wife Barbara November 1, 1978 in Hoston, TX. Bush is campaigning for the presidential primary elections. (Photo by Dirck Halstead/Liaison)
Republican vice-Presidential candidate George Bush and wife, Barbara, welcomed home to Houston, Monday, Nov. 3, 1980 by three-year old granddaughter, Noelle, who was on hand to meet the plane. Bush will have a final home rally and vote in Houston. (AP Photo/Bill Hudson)
American politician (and future US President) George HW Bush speaks at an event during his campaign for the Republican Presidential nomination, Iowa, January 1980. His wife, future First Lady Barbara Bush, stands beside him. (Photo Robert R. McElroy/Getty Images)
NBC NEWS -- 'Ronald Reagan First Presidential Inauguration' -- Pictured: (l-r) U.S. Vice President George Bush, Second Lady Barbara Bush during the first inauguration of President Ronald Reagan on January 20, 1981 in Washington D.C. -- (Photo by: NBC News/NBCU Photo Bank via Getty Images)
373930 01: Vice President George Bush stands with his wife Barbara August 1983 in Kennebunkport, ME. Bush is vacationing in Maine with his family. (Photo by Cynthia Johnson/Liaison)
Bush, George & Mrs. (Barbara); (Photo By Jerry Cleveland/The Denver Post via Getty Images)
Republican presidential candidate George Bush and his wife Barbara stand together on the podium during the finale of the Republican National Convention in New Orleans, Aug. 18, 1988. (AP Photo/Ron Edmonds)
President-elect George Bush and his wife Barbara are shown during a morning beachfront news conference in Gulf Stream, Fla., Nov. 14, 1988. Bush is expected to return to Washington Tuesday after a long weekend vacationing in Florida. (AP Photo/Kathy Willens)
US President George Bush and his wife Barbara wave goodbye from the steps of Air Force one at London's Heathrow Airport, Friday, June 21, 1989, prior to their departure for the United States. President Bush left London on Friday morning at the end of a European visit which included stops at Rome Brussels. Bonn and London. (AP Photo/Dave Caulkin)
Pres. George H. W. Bush, left, talks to reporters on Air Force One as First Lady Barbara Bush, right, looks on, Feb. 9, 1990. Bush defended his military bases and tough talk on defense issues at a time of dramatic changing on in Moscow, saying the timing happened to be fortuitous. (AP Photo/Robert Daugherty)
U.S. President George H. Bush smiles as First Lady Barbara Bush waves as they leave the tarmac following their arrival at Helsinki airport, Wednesday, night, July 8, 1992. Bush arrived Wednesday for a 51-nation summit to plan peacekeeping, economic revival and the growth of democracy in post-Cold War Europe. (AP Photo/Doug Mills)
President George H.W. Bush and first lady Barbara Bush join in song during an ecumenical prayer breakfast in Houston, Aug. 20, 1992. Bush will deliver what could be the speech of his life at the Astrodome Thursday as he accepts the nomination of the Republican Party to serve a second term. (AP Photo/James Finley)
Former President George Bush shows off the James Forrestal award he received in Washington, Thursday, March 18, 1993, as his wife Barbara looks on. The award is given annually by the National Security Industrial Association to an American whose leadership has promoted understanding and cooperation between industry and government. It was the Bushes first return to Washington since leaving the White House. (AP Photo/Stephen R. Brown)
Former President George Bush and his wife, Barbara, are shown in this image from a television monitor Monday, Jan. 22, 1996, in Houston, in a television campaign to help sell season tickets for the Houston Astros. In the campaign, set to debut Jan. 29., the former first couple are seen recalling Bush's days as a first baseman for Yale. (AP Photo/Houston Astros)
Former first lady Barbara Bush, left, ponders what advice she would give her sons if any of them became president after being asked by a student during a question and answer session while being honored with her husband, former president George Bush, at Washington College in Chestertown, Md., Friday, Jan. 29, 1999. Both received honorary degrees of Doctor of Public Service. (AP Photo/John Gillis)
Former President George W. Bush and his wife Barbara pose for photographers prior to AmeriCares Celebration of Hope, 20th Anniversary Gala in New York Tuesday, May 21, 2002. (AP Photo/Osamu Honda)
Former U.S. president George Bush smiles at his wife Barbara, as he holds a golden wreath behind her head during their visit to see U.S. athletes training at the American college in Athens, Friday, Aug. 13, 2004. The wreath was presented to the former president by the college. Bush will visit the Athens 2004 Olympic Games starting in the evening. (AP Photo/Thanassis Stavrakis)
Former President George H. W. Bush, left, and his wife Barbara, sit together in Madison Square Garden during the Republican National Convention in New York, Wednesday, Sept. 1, 2004. (AP Photo/Ed Reinke)
Former President George H. W. Bush reacts to the crowd with his wife Barbara Bush at the Commander-In-Chief Ball in Washington Thursday, Jan. 20, 2005. (AP Photo/Gerald Herbert)
Former U.S. President George Bush, right, and wife Barbara attend a Houston Astros baseball game against the Milwaukee Brewers, Sunday, May 4, 2008, in Houston. (AP Photo/Pat Sullivan)
Former President George H.W. Bush and former first lady Barbara Bush arrive for a ceremony to dedicate an expanded gallery that carries his name at the National Museum of the Pacific War, Monday, Dec. 7, 2009, in Fredericksburg, Texas. The 41st president, who lives in Houston, is a former World War II naval aviator who survived being shot down over the Pacific. (AP Photo/Eric Gay)
Former U.S. President George H.W. Bush, right, and his wife, Barbara, cheer for the Houston Astros during the fourth inning of a baseball game against the Arizona Diamondbacks, Wednesday, May 5, 2010, in Houston. (AP Photo/David J. Phillip)
Former first lady Barbara Bush touches the hair of her husband President George H.W. Bush as they arrive for the premiere of HBO's new documentary on his life near the family compound in Kennebunkport, Maine, Tuesday, June 12, 2012. The premiere was held on the president's 88th birthday. (AP Photo/Charles Krupa)
Former President George H.W. Buch and wife Barbara take part in throwing out the ceremonial first pitch before Game 3 of baseball's American League Division Series between the Kansas City Royals and Houston Astros Sunday, Oct. 11, 2015, in Houston. (AP Photo/Patric Schneider)
Discover More Like This
BACK TO SLIDE
Bush ended the letter assuring Clinton that he was on his side. "Your success now is our countries success," he said. "I am rooting hard for you."
Bush's kind words have not only resurfaced all these years later, but they are going viral. This tweet containing the letter has garnered thousands of likes and retweets, for example. Many replied, feeling wistful for past elections:
@sabagl This to the guy of beat him. It feels like something written a million years ago...