Sen. Claire McCaskill (D-Mo.) speaks to constituents during a roundtable. (Julie Denesha/For The Washington Post)

Sen. Claire McCaskill (D-Mo.) has signed her name to an effort to draft Hillary Clinton into the 2016 presidential race, becoming the first sitting member of Congress to do so.

The Ready for Hillary super PAC announced McCaskill as its latest big-name supporter on Tuesday morning. McCaskill in 2008 supported President Obama over Clinton in the primary, but said earlier this year that she hopes Clinton will run again.

"Hillary Clinton had to give up her political operation while she was making us proud, representing us around the world as an incredible Secretary of State, and that’s why Ready for Hillary is so critical,” McCaskill said in a statement provided by Ready for Hillary.

Other supporters of the effort include longtime Clinton strategists James Carville and Harold Ickes. Top former Clinton aides and fundraisers have also lent their names to the effort.