Eighteen Senate Republicans are bucking a majority of their party and former President Donald J. Trump in joining Democrats to push military assistance for Ukraine toward approval in the Senate, highlighting a widening foreign policy divide in the contemporary Republican Party.
The 18 senators, mainly national security hawks who include several military veterans, have provided the votes necessary to overcome multiple filibusters backed by a majority of their colleagues, clearing the way for approval within days of $95 billion in aid to Ukraine, Israel and allies in the Pacific region.
“The thread that binds that group together is national security,” said Senator Jerry Moran, a Kansas Republican who is one of the 18. “America’s national security, the belief that what happens in Ukraine matters to the United States, the belief that what happens in Israel matters and the belief that what happens in the South Pacific matters.”
Backing the funding could draw condemnation from Mr. Trump and his allies, a possibility that was most likely a factor in the decision of some to oppose it.
Some Republicans who have balked at the bill have suggested that they could ultimately back the legislation on final passage after trying to use their opposition to win the chance to change it — an effort that has so far not proved successful. But whether more than half of the 49 Republicans will vote for it remains an open question.
Here’s a closer look at the defectors so far, and what is motivating them.
All but two of the Senate’s Republican leaders
The group includes the two top Senate Republicans, Mitch McConnell of Kentucky and John Thune of South Dakota, as well as two others on the leadership team: Senators Joni Ernst of Iowa and Shelley Moore Capito of West Virginia.
Two other leaders, Senators John Barrasso of Wyoming and Steve Daines of Montana, both of whom have endorsed Mr. Trump, are opposed.
The sharp split on the funding inside the top echelons of the Senate Republican Conference mirrors a sharp division inside the party, which for much of the post-World War II era has been a strong proponent of exerting American power overseas and standing by U.S. allies. But there is a growing and strong sentiment among Republicans — encouraged by Mr. Trump — of withdrawing from foreign involvement.
Mr. McConnell has been among the most vocal proponents of sending aid to Ukraine. He has called Kyiv’s war against Russian aggression an existential issue and argued with increasing fervor in recent days that the United States must not abandon its democratic ally standing up against President Vladimir V. Putin.
Senator Rand Paul, a Kentucky Republican who has been leading an effort to slow-walk the military assistance measure, on Monday called the idea that bolstering Ukraine was essential to America’s national security “ludicrous.”
“I think sending money to Ukraine actually makes our national security more endangered,” Mr. Paul said. “The leadership has come together, but it is the wrong kind of compromise. It is a compromise to loot the Treasury. They are shoveling out borrowed cash.”
Others who voted for the funding include Senators John Cornyn of Texas, a former top Republican who is interested in rejoining leadership, and Charles E. Grassley of Iowa, the longest-serving Senate Republican.
National security leaders and veterans
Several members of the Armed Services Committee have backed moving ahead with the bill, including Senator Roger Wicker of Mississippi, the senior Republican on the panel. Other members of that committee who voted to advance the military assistance are Senator Mike Rounds of South Dakota, Ms. Ernst and Senators Dan Sullivan of Alaska and Markwayne Mullin of Oklahoma.
Ms. Ernst served overseas as an Iowa National Guard officer, and Mr. Sullivan is a colonel in the Marine Corps Reserve. A third Republican veteran who has been a strong backer of the aid, Senator Todd Young of Indiana, is a former Marine officer.
Democrats have praised the 18 Republicans who have joined them in the Ukraine effort.
“I think they understand the necessity of supporting Ukraine, particularly since this is a contest between a rules-based international order and Russian autocracy,” said Senator Jack Reed, Democrat of Rhode Island and the chairman of the Armed Services Committee. “They also understand that it could involve our service members soon.”
Mainstream Republicans and appropriators
Members of the Appropriations Committee, including two more-centrist senators — Susan Collins of Maine, the senior Republican on the spending panel, and Lisa Murkowski of Alaska — have also been instrumental in pushing the aid. Other appropriators behind the bill include Mr. Moran, Senator John Kennedy of Louisiana and Ms. Capito.
The measure has the backing of a handful of others who have been known to break with their party and support bipartisan compromises, including Senators Mitt Romney of Utah, a member of the Foreign Relations Committee; Bill Cassidy of Louisiana; and Thom Tillis of North Carolina.
“I think there is a common understanding that if we fail on this vote, if we don’t support Ukraine — this is not bluster, this is not hyperbole — bad things are going to happen,” Mr. Tillis said on Monday.
Republican backers of the legislation say they cannot worry about Mr. Trump or the potential electoral consequences given the urgency behind the push to restrain Russia and avoid a wider war in Europe or Asia.
“The stakes are high, and we must meet the moment,” Ms. Collins said.
As far a potential backlash, Mr. Tillis said he was not worried.
“I slept like a baby last night,” he said, referring to his vote on Sunday to overcome the filibuster by a majority of his Republican colleagues.
The following is an alphabetical list of the 18 Republicans who voted to advance the bill past a critical procedural hurdle on Sunday:
Senator Shelley Moore Capito of West Virginia
Senator Bill Cassidy of Louisiana
Senator Susan Collins of Maine
Senator John Cornyn of Texas
Senator Joni Ernst of Iowa
Senator Charles E. Grassley of Iowa
Senator John Kennedy of Louisiana
Senator Mitch McConnell of Kentucky
Senator Jerry Moran of Kansas
Senator Markwayne Mullin of Oklahoma
Senator Lisa Murkowski of Alaska
Senator Mitt Romney of Utah
Senator Mike Rounds of South Dakota
Senator Dan Sullivan of Alaska
Senator John Thune of South Dakota
Senator Thom Tillis of North Carolina
Senator Roger Wicker of Mississippi
Senator Todd Young of Indiana