Senator Mitch McConnell, the longtime top Senate Republican, said on Wednesday he would give up his spot as the party’s leader at the end of this year, acknowledging that his Reaganite national security views had put him out of step with a party now headed by former president Donald J. Trump.

“Believe me, I know the politics within my party at this particular time,” Mr. McConnell, who turned 82 last week, said in a speech on the Senate floor announcing his intentions. “I have many faults. Misunderstanding politics is not one of them.”

His decision, reported earlier by The Associated Press, was not a surprise. Mr. McConnell suffered a serious fall last year and experienced some episodes where he momentarily froze in front of the media. He has also faced rising resistance within his ranks for his push to provide continued military assistance to Ukraine as well as his close-to-the-vest leadership style.

Mr. McConnell had said earlier that he would serve out his full Senate term ending in 2026, but had been more opaque about whether he would try to remain leader after the November elections.

His announcement followed a White House meeting on Tuesday where he strongly advocated congressional passage of a foreign aid bill that includes more than $60 billion in aid for Ukraine and urged Speaker Mike Johnson, his Republican counterpart, to put the proposal on the House floor.