Senator Mitch McConnell put his standing on the line in aggressively pursuing military assistance for Ukraine over deep Republican resistance, and he achieved the outcome he wanted: a strong Senate vote to bolster embattled U.S. allies at a critical moment.

“History settles every account,” Mr. McConnell, Republican of Kentucky and the minority leader, said in a statement issued early Tuesday, minutes after the Senate voted 70 to 29 for a $95 billion foreign aid package. “And today, on the value of American leadership and strength, history will record that the Senate did not blink.”

But his hard-fought legislative victory came at a cost.

The bitter Senate fight over the aid package — money that Mr. McConnell framed as essential to preserving Western power — exposed serious divisions among Senate Republicans not just over Ukraine and border security policy but over his leadership.

The fallout underscored Mr. McConnell’s waning influence over his party’s rank and file and raised new questions about his future. Though most of his chief critics had weighed in against him in the past, their complaints took on a bold new intensity as they openly called for his ouster and contended he was out of step with a majority of his colleagues, as evidenced by the fact that most Republicans opposed the bill.

“It stinks to high heaven,” Senator J.D. Vance, a freshman Republican from Ohio, declared on the Senate floor on Monday. “No one who watched this process unfold believes Republican leadership negotiated in good faith for border security or that Democrats did the same. It was always Kabuki theater.”

But Mr. McConnell, a traditional Reaganite interventionist on foreign policy, was determined to secure more money for Ukraine even though it put him on a collision course with many of his Republican members and former President Donald J. Trump, the party’s likely 2024 nominee.

In speech after speech leading up to the vote, Mr. McConnell was adamant that the United States had no choice but to keep supplying Ukraine to hold off Russian invasion, with his appeals increasingly aimed at naysayers as the debate in the Senate intensified.

“In this chamber, we must face the world as it is,” Mr. McConnell said on Sunday in arguing for the legislation. “We must reject the dimmest and most shortsighted views of our obligations and grapple instead with actual problems.”

He was so fixed on securing the Ukraine money that he reluctantly acceded to conservative demands that approval be tied to Congress enacting new restrictions at the southern border, a link he acknowledged would be challenging to achieve. He proved correct. After his staff took part in lengthy negotiations to produce a new border measure, those same conservatives quickly repudiated it, and Mr. McConnell ended up voting against what was essentially his bill.

The Senate then pivoted to considering the $60 billion in Ukraine aid along with assistance for Israel and Pacific allies with the border provisions stripped away. Mr. McConnell voted repeatedly to overcome Republican filibusters. Despite the Senate win, the prospects for the legislation in the House were very uncertain given resistance by far-right Republicans who have denounced Mr. McConnell as a globalist leader of a “uniparty.”

Republican critics said Mr. McConnell’s problem was that he had more in common with Democrats led by Senator Chuck Schumer of New York, the majority leader, when it came to the border and Ukraine policy than with his fellow Republicans. They said he undermined the party’s political cause by providing Democrats cover on a failure to secure the border.

“Republican leadership strategy has been a disaster from the outset on this immigration deal,” said Senator Ted Cruz, Republican of Texas. He added that Mr. McConnell was “echoing word for word the talking points of Chuck Schumer and the Democrats.”

It was a dynamic Mr. Schumer captured at a recent black-tie congressional media dinner, when he cracked a joke about his alliance with Mr. McConnell that played off a Jay-Z lyric.

“I guess you could say I got 99 problems, but Mitch ain’t one,” Mr. Schumer quipped.

Other Republicans backed Mr. McConnell, saying he pursued the policy out of principle and a desire to protect America’s place in the world despite angry conservative blowback.

“Nobody here can blame Mitch,” said Senator Thom Tillis, Republican of North Carolina and a backer of the bill. “I completely support him.”

“It’s not a Mitch problem,” said Senator Lindsey Graham, Republican of South Carolina, who opposed the legislation. “It is just the way the system works. You have division on Ukraine.”

Mr. McConnell has been under fire before and faced a challenge to his leadership post last year that he easily dispatched. But members of the growing contingent of more aggressive, MAGA-aligned Senate Republicans have been unsparing in their assessment of his handling of the border and Ukraine fights, saying he was too focused on rescuing Ukraine and not enough on needs at home.

“This has just been such an absolute debacle,” said Senator Josh Hawley, Republican of Missouri.

“His problem is he doesn’t talk to his members; he doesn’t listen to his members,” Mr. Hawley told reporters recently. “Is it any wonder that Republicans are up in arms?”

Senator Rand Paul, McConnell’s home-state Republican colleague and a frequent critic, was caustic in his assessment of the minority leader as he assailed the foreign aid package.

“The leadership in the Republican Party is really not a great deal,” Mr. Paul said. He took issue with one of Mr. McConnell’s main arguments in support of Ukraine funding: that much of the federal money ultimately finds its way to U.S. companies that manufacture weapons and ammunition. “I find it really disturbing that there are people out there making the argument on both sides of the aisle, ‘No big deal, it’s helping our defense industrial base.’”

Mr. McConnell reached a personal goal of becoming the longest-serving Senate leader in January 2023, when he began his 17th year as the top Republican. But it has been a difficult stretch since then for Mr. McConnell, who suffered a serious fall in March and experienced some very public health episodes that prompted questions about whether he could continue in his post.

Mr. McConnell, who turns 82 next week, has said he intends to serve out his Senate term, which ends at the start of 2027. But he has been less definitive about whether he will run again for leader after the elections in November.

Senators close to Mr. McConnell say they believe he would relish the chance to return a last time as majority leader if Republicans can recapture the Senate. But the past few weeks provided a demonstration of how difficult it would be to remain leader if Mr. Trump — a harsh foe of his — was in the White House aligned with an aggressive anti-McConnell MAGA faction in the Senate.

“I don’t know what he might want to do,” Senator Kevin Cramer, Republican of North Dakota, said about Mr. McConnell’s future as leader. “What I can’t imagine is why he would want to run again.”