(CNN) Missouri Sen. Claire McCaskill said on Thursday that she may face a primary before the 2018 mid-term elections, comparing calls for ideological purity from the Democratic base to the conservative Tea Party movement of the Obama era.

"I am for sure gonna run," McCaskill said on "The Mark Reardon Show" on KMOX Newsradio 1120. "And I may have a primary because there is, in our party now, some of the same kind of enthusiasm at the base that the Republican party had with the Tea Party. We are seeing that same--and many of those people are very impatient with me because they don't think I'm pure. For example, they think I should be voting against all of Trump's nominees and of course I'm judging each nominee on its own merit."

McCaskill is among a group of red state Democrats up for reelection in 2018 that also includes Indiana Sen. Joe Donnelly, Montana Sen. Jon Tester, West Virginia Sen. Joe Manchin, and North Dakota Sen. Heidi Heitkamp.

In Thursday's interview, she told the St. Louis radio station it was "too early" to know how she'd vote on Neil Gorsuch, Trump's pick to fill the vacant seat on the Supreme Court. She added that while she was making decisions about Trump's nominees based on individual merits, that wasn't "good enough" for some members of her party.

"As of today it's about half and half of the ones I've voted no on and the ones I've voted yes on and I'm making an individual decision based on merit on each one," McCaskill said. "That's not good enough for some of these folks who want me to be just against Trump everywhere. On the other hand, you know, I do think that I was humbled and I realized that there's a whole lot of people in Missouri that fundamentally think Washington, DC, is not paying any attention to their needs. My party's not talking to them about what they're worried about. I hear that loud and clear and I'm gonna work as hard as I can to show respect for those folks and to listen and to try to do better and correct mistakes that I may have made in terms of serving them as well as I possibly can."

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