McCaskill becomes first lawmaker to endorse Ready for Hillary PAC

Sen. Claire McCaskillClaire Conner McCaskillGovernment watchdog finds safety gaps in assisted living homes GOP Senate candidate fundraising lags behind Dems in key races McCaskill challenger links human trafficking to 'sexual revolution' of 1960s MORE (D-Mo.) on Tuesday endorsed the Ready for Hillary super-PAC, becoming the first lawmaker to back an effort aimed at pushing Hillary ClintonHillary Diane Rodham ClintonTrump touts report Warner attempted to talk to dossier author Poll: Nearly half of Iowans wouldn’t vote for Trump in 2020 Rubio on Warner contact with Russian lobbyist: It’s ‘had zero impact on our work’ MORE to run for president in 2016. [WATCH VIDEO]

McCaskill called the super-PAC's efforts "critical" to electing Clinton if she decides to seek the Democratic nomination.

“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. 

“It’s important that we start early, building a grassroots army from the ground up and effectively using the tools of the Internet — all things that President Obama did so successfully — so that if Hillary does decide to run, we’ll be ready to help her win.”

Ready for Hillary is the main political action committee unofficially supporting Clinton's possible bid. Its efforts have been focused largely on grassroots organizing and fundraising, and the group hopes to build a strong volunteer force nationwide to support Clinton if she mounts a campaign.

McCaskill praised the group for working to expand Clinton's base of support, noting that it's reaching out to more than just her 2008 presidential supporters.

"They’re helping to show that regardless of who you supported for president back then, we can all agree today that there is nobody better equipped to be our next president than Hillary Clinton," she said.

McCaskill was an early backer of President Obama in 2006 ahead of his primary fight against Clinton. 

During her Senate run in 2006, she said she wouldn't let her daughter near former President Bill ClintonWilliam (Bill) Jefferson ClintonLongtime Clinton confidant blames Comey for 2016 loss Trump’s national monument rollbacks take effect A year after Obama, Dems still looking for replacement MORE, a remark that led to the cancellation of a Clinton fundraiser for McCaskill, according to the book Game Change.

Though she sent letters of apology to the Clintons and won her race, the relationship remained strained through the 2008 elections, as McCaskill backed Obama.

Ahead of 2016, McCaskill has been an early supporter of Clinton. 

She previously endorsed Clinton's potential presidential run on the day Clinton retired as secretary of State, saying in a statement that "if her future plans include seeking the presidency, which I hope they do, then I look forward to being on her team and working my heart out to see her elected."

The Ready for Hillary group’s founders are longtime Clinton loyalists who have helped on previous campaigns but aren’t in her inner circle. 

But in the months since its launch, the super-PAC has signed on a number of advisers who have closer ties to the Clintons, including Bill Clinton’s former White House Political Director Craig Smith, former Rep. Ellen Tauscher (D-Calif.) and Harold Ickes, a senior adviser on Hillary Clinton’s 2008 presidential run.