The White House just took Hillary Clinton's side in her latest fight with Bernie Sanders

The White House came to the defense of Democratic presidential frontrunner Hillary Clinton on Thursday, one day after rival Bernie Sanders charged that the former secretary of state is "not qualified" to serve as president.

Speaking to reporters aboard Air Force One as President Barack Obama flew to Chicago, deputy press secretary Eric Schultz said, Obama sees his 2008 primary opponent as a qualified successor.

Clinton "comes to the race with more experience than any non-vice president" in recent history, Schultz said, according to a pool report.

Schultz added that Obama was "fortunate" that Clinton agreed to become his chief diplomat after the two bitterly sparred during the 2008 primaries.

See Clinton and Sanders at the Las Vegas town hall:

Sanders himself thought much the same thing at the time of Clinton's nomination, as she pointedly noted on Twitter Thursday:

Now, the Vermont senator is sounding a sharply different tune. Stumping in Philadelphia on Wednesday evening, Sanders charged that Clinton's support from super PACs and her past advocacy of the Iraq War and free trade agreements rendered her "not qualified" for the Oval Office.

Sanders leveled the charge because, he alleged, Clinton "has been saying lately that she thinks that I am, quote unquote, not qualified to be president," although Clinton has never made that explicit assertion, even as she says he hasn't "done his homework" on his policy proposals.

A contentious relationship: The administration's pushback against Sanders' remarks is but the latest development in an often-tense relationship between the president and the progressive insurgent.

Unsatisfied with Obama's record on progressive economic issues, Sanders encouraged a left-wing primary challenge to the president in 2012, and it's hard not to hear his denunciations of a "rigged" economy as, in part, an indictment of the incumbent's policies.

Seeking to woo Democratic voters, however, Sanders has lately offered warmer words for Obama, declaring that the administration has "moved this country forward" despite "incredible Republican obstruction."

But Obama has kept his distance from Sanders, suggesting in a Politicointerview that Sanders is too focused on inequality to the detriment of other issues and reportedly telling a recent fundraiser that the clock is running out on the senator's campaign.