These 20 GOP senators still haven't endorsed Trump — and some of them probably never will

• Trump is the likely GOP nominee, and most Republican senators have endorsed him.
• But there's still a rather conspicuous group of holdouts.
• A few voted to convict Trump and may never back him, while others will do so once he's the nominee.

After victories in both Iowa and New Hampshire, former President Donald Trump's ascent to the Republican nomination in 2024 is all but certain — even as Nikki Haley vows to continue her campaign.

That reality has spurred a rush of endorsements from members of Congress in recent days and weeks, bringing Trump to a solid majority among Republicans in both chambers while leaving Haley with just one: Rep. Ralph Norman of South Carolina.

Yet in the Senate, long a bastion of Republican resistance (or at least hesitancy) to Trump, there are still a number of holdouts.

As of January 24, there are still 20 Republican senators — out of 49 total — who have not endorsed Trump's 2024 bid.

Some of those senators can be expected to get behind Trump when his nomination becomes official, or at least uncontested. Even Mitch McConnell, the Senate Minority Leader known to have a frosty relationship with the former president, has said that he'll back Trump if he's the nominee.

But there are at least a few who may never get behind their party's nominee. Four current GOP senators — Bill Cassidy of Louisiana, Susan Collins of Maine, Lisa Murkowski of Alaska, and Mitt Romney of Utah — voted to convict Trump for incitement of an insurrection following January 6.

But it's not just those four: Others, such as Sen. Todd Young of Indiana, have expressed staunch resistance to supporting Trump in 2024.

"Are you trying to get a gut check — am I joining everyone else in joining the Trump establishment? Hell no," Young told reporters ahead of the New Hampshire primary.

Yet GOP lawmakers have faced pressure, both from Trump and their voters, to fall in line. And further resistance to the former president could have negative consequences for them if Trump were to end up winning this year.

"The biggest risk is that voters see them as disloyal to the party's core message going in 2024," Sen. JD Vance of Ohio, an early Trump endorser, told POLITICO in January. "That is a real risk. And that's why I've encouraged a lot of folks to endorse the former president."

Here are the 20 GOP senators who haven't endorsed Trump:

• John Boozman of Arkansas

• Shelly Moore Capito of West Virginia

• Bill Cassidy of Louisiana

• Susan Collins of Maine

• Joni Ernst of Iowa

• Chuck Grassley of Iowa

• Ron Johnson of Wisconsin

• John Kennedy of Louisiana

• James Lankford of Oklahoma

• Mitch McConnell of Kentucky

• Jerry Moran of Kansas

• Lisa Murkowski of Alaska

• Rand Paul of Kentucky

• Pete Ricketts of Nebraska

• Mitt Romney of Utah

• Mike Rounds of South Dakota

• Dan Sullivan of Alaska

• John Thune of South Dakota

• Thom Tillis of North Carolina

• Todd Young of Indiana

This story will be updated as this list inevitably shrinks.