Former President Barack Obama will return to politics in May when he appears at a fundraiser for vulnerable Democratic Sen. Claire McCaskill, NBC News confirms. 

Obama will help raise cash for the Missouri Democrat in Beverly Hills on May 6, according to a source familiar with the matter. It will be the first appearance the former president has made on behalf of a Democratic candidate since leaving the White House. 

McCaskill, running for re-election in a state Donald Trump won by 19 points in 2016, is a top target for Republicans this fall. 

She was the first female senator to endorse Obama during his 2008 run, backing the then-Illinois senator over Hillary Clinton. McCaskill went on to become one of Clinton's most prominent early backers during her 2016 run.