Sen. Jon Tester, D-Mont., is skipping a meeting with President Biden's campaign advisers on Thursday and will not elaborate on his reasoning as concerns about Biden's fitness grow in Congress. 

The at-risk Montana Democrat told reporters on Wednesday he wouldn't be going to the special meeting at the Democratic Senatorial Campaign Committee (DSCC) with senior Biden advisers Mike Donilon and Steve Ricchetti, and campaign chair Jen O'Malley Dillon, which was announced that afternoon. 

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He didn't say why he wasn't going, and his office said Tester had "a scheduling conflict," but declined to answer questions from Fox News Digital about the details of the conflict. 

Sen. Tim Kaine, D-Va., also won't be joining the special meeting. He is running for re-election in Virginia, a state that has recently seen a trend in favor of former President Trump as widespread worry over Biden's condition endures. 

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Kaine told reporters on Wednesday he was not sure if he would be able to attend because of his plans to campaign in Virginia, which is a short commute from the Capitol. 

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"Senator Kaine had a previously scheduled event planned during this time that could not be moved," a spokesperson for Kaine's campaign told Fox News Digital. "As you saw yesterday, this event was planned last minute and with such little notice we could not adjust to make the event at the DSCC." 

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Sen. Martin Heinrich, D-N.M., will be going to the event with Biden's team. He is also facing re-election in November. Heinrich didn't answer questions from Fox News Digital about Biden's fitness to be president on Tuesday, holding up a phone to his ear in an apparent call. 

The campaigns and Senate offices of Sens. Sherrod Brown, D-Ohio, Bob Casey, D-Pa., Jacky Rosen, D-Nev., Tammy Baldwin, D-Wis., Amy Klobuchar, D-Minn., and Kirsten Gillibrand, D-N.Y., did not immediately provide comment to Fox News Digital when asked if they would be attending.