Some of the most vulnerable Senate Republicans facing reelection this fall could be missing from Donald Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE's meeting with the Senate GOP on Thursday.

Sens. Kelly Ayotte Kelly Ann AyotteBottom line Bottom line Bottom Line MORE (R-N.H.) and John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.) won't be at the meeting because of a conflicting Senate Armed Services Committee hearing.

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"I'm chairman of the Armed Services Committee," McCain told reporters. "We scheduled this hearing a couple of months ago. So I can't just walk out of there."

Ayotte told The Wall Street Journal that the committee meeting would also keep her from attending the closed-door meeting with Trump at the National Republican Senatorial Committee.

Thursday's meeting comes ahead of the GOP convention in Cleveland, which many Republican senators have said they will skip.

Asked if he would attend the Thursday meeting with Trump, Toomey told reporters he would need to check his schedule. Portman also said Wednesday that he needs to check and see if he has any previously scheduled events, NBC News reported

Rubio, who reversed course and announced late last month that he would run for reelection, said he is scheduled to preside over the Senate.

Paul, asked if he would attend, said he was largely unfamiliar with the meeting.

Rubio, Toomey, Portman, Kirk and Ayotte each face tough reelection bids in states previously carried by President Obama.

Democrats have raced to link them to Trump, arguing his controversial comments will drag down vulnerable GOP lawmakers.

Republicans are defending 24 Senate seats in November. Democrats need to flip five seats — or flip four and retain the White House — to win back control of the Senate.

--Julian Hattem contributed