By Susan Cornwell
WASHINGTON, July 14 (Reuters) - Democrats could take a step toward wresting control of the U.S. Senate from Republicans on Tuesday when voters in Maine, Texas and Alabama cast ballots in nominating contests.
Maine Democrats pick a challenger to Susan Collins, one of the Senate's most at-risk Republicans; Texas Democrats choose who will go up against Republican Senator John Cornyn in a Republican-leaning state analysts say has become more competitive, and Alabama Republicans pick a candidate to take on Doug Jones, widely considered the chamber's most vulnerable Democrat.
Republican President Donald Trump's public approval has dropped as the coronavirus pandemic surged through the United States, killing more than 130,000 people and throwing tens of millions out of work.
That is weighing on his fellow Republicans, dimming the re-election hopes of senators in Colorado, North Carolina and Arizona and leaving even senior Republicans in conservative stakes like Mitch McConnell's Kentucky having to work harder than expected to defend their seats.
Democrats would need to pick up four seats in the 100-member chamber for a majority if Trump is re-elected, or three if presumptive Democratic nominee Joe Biden wins the White House, giving the party a tie-breaking Senate vote.
"If the coronavirus continues to get worse and the economy doesn't improve, it's hard to imagine any president ... getting re-elected very easily, and it's hard to imagine that president's party doing well," said Joshua Blank, research director of the Texas Politics Project at the University of Texas at Austin.
TOP DEMOCRATIC OPPORTUNITY
Democrats see Collins' Senate seat representing Maine as one of their top pick-up opportunities. Democrat Sara Gideon, the speaker of the Maine House of Representatives, has been leading Collins by a few percentage points in recent opinion polls even before Tuesday's primary between Gideon and two more left-wing Democrats, Betsy Sweet and Bre Kidman.
Collins is a moderate Republican first elected in 1996 who has long enjoyed a reputation for bipartisanship in a state with many independent voters. Her support eroded after she sided with Trump in several votes, including backing his Supreme Court nominee Brett Kavanaugh in 2018.
Collins' vote for Kavanaugh served to "enrage many Mainers, and it's caused a different reaction to Collins than there ever really has been before," said Mark Brewer, political science professor at the University of Maine.
In Texas, state Senator Royce West and Air Force veteran MJ Hegar are battling in a runoff race for the Democratic nomination to take on Cornyn.
The growth of young non-white populations on the outskirts of Texas' urban areas has made the state long dominated by Republicans more competitive, Blank said. Biden has built a five-point lead over Trump in Texas, a Dallas Morning News/University of Texas at Tyler poll said Sunday.
The voting in all three states was delayed by the coronavirus pandemic.
Related: President Trump in 2020
DEMOCRATS PLAY DEFENSE IN ALABAMA
In Republican stronghold Alabama, Republicans will pick between Jeff Sessions - a former U.S. attorney general fired by Trump who now wants his old Senate job back - or political newcomer Tommy Tuberville, a former Auburn University football coach endorsed by Trump.
A poll from Auburn University at Montgomery last week said Tuberville is 15 points ahead of Sessions. The results also showed the incumbent, Jones, faces a difficult battle for re-election against either Sessions or Tuberville, said poll director David Hughes.
In a 2017 special election, Jones became the first Democrat to win a Senate seat from Alabama in a quarter century after defeating Roy Moore, whose campaign was derailed by accusations of sexual misconduct with teenage girls.
"Look, we've won when no one thought we could win," said Joe Trippi, strategist for the Jones campaign. "Most of the conventional wisdom out there about Alabama and this race is wrong." (Reporting by Susan Cornwell; Editing by Scott Malone and Cynthia Osterman)