Sen. Claire McCaskillClaire Conner McCaskillThe Hill's Morning Report — Can the economy help Republicans buck political history in 2018? Dems seek to leverage ObamaCare fight for midterms Dems say Obama return from sidelines is overdue MORE (D-Mo.) said Thursday that former Secretary of State Hillary ClintonHillary Diane Rodham ClintonThere are many unanswered questions about FBI culture FBI agent who sent anti-Trump texts offers to testify on Capitol Hill Giuliani wants 'full and complete' investigation into Russia probe's origins MORE called her earlier this week after she endorsed an effort to draft the former first lady into the 2016 presidential race.

"She did call me after this all happened the other day, and we had a great conversation," McCaskill, the first sitting lawmaker to throw her support behind Clinton, told MSNBC's "Morning Joe."

McCaskill said she would not give details of the private conversation, but the call could add to the speculation about Clinton contemplating a White House run.

"I think she has a big decision to make, and I think she's in the process of making it," McCaskill said.

Still, the Missouri senator said she was surprised at the attention given to her endorsement of the Ready for Hillary political action committee.

"It was interesting how this kind of blew up the other day — it doesn't seem complicated to me," she said. "She is by far the strongest, most capable, most qualified candidate for president of the United States."

McCaskill was noncommittal when asked whether she would approach wealthy donors to help fund the PAC's efforts to draft the former secretary of State, noting that she had just finished a tough Senate campaign.

"I just came out a vortex of pressure in terms of raising campaign cash," McCaskill said, adding that the group was concerned more with building up a volunteer infrastructure than raising money.

"This is really about building an effort from the ground up."

The senator and the Clintons have had a rocky relationship; McCaskill was an early supporter of President Obama during the 2008 Democratic primary fight.

During her 2006 Senate race, McCaskill also criticized former President Clinton, saying that she would not allow her daughter near him, a remark that led the Clintons to cancel a fundraiser for her.