Just slightly more than a third of the 21 Republican senators up for re-election this year say that they'd unquestionably support Donald Trump if he becomes the party's presidential nominee, according to a month-long survey by NBC News.
Eight of these senators--including those facing both safe and competitive contests--have responded that they'd back Trump.
"I'll support the nominee. I think any of our candidates would be a better president than Secretary Clinton or Senator Sanders," Sen. Roy Blunt, R-Mo, said.
One of the Senate's most vulnerable candidates, Sen. Mark Kirk from Illinois, recently told NBC's Chicago affiliate that if Trump were to clinch the nomination he "certainly would" support him.
Another six GOP senators up for re-election have hedged on whether they'd stand behind Trump if he's the nominee, opting instead to observe the rest of the Republican primary season.
A spokeswoman for Sen. Kelly Ayotte, R-N.H., who's facing a tough challenge in November, said "Sen. Ayotte intends to support the Republican nominee, however, she would like to see how the process plays out."
"I've always said I was going to support the nominee," said Sen. Richard Burr, R-N.C. "I'm hopeful I'll be able to support the nominee."
Despite some hesitancy by a few senators, none of the 21 senators facing re-election said they would actively oppose Trump if he becomes the party's nominee.
As for the remaining seven senators, they and their offices refused to answer the question, despite multiple attempts by NBC News.
This survey was conducted by contacting these senators' offices and campaigns at least twice in the past month, as well as by monitoring their past statements. Here are the results:
Senators backing Trump (8)
John Boozman (AR)
Campaign spokesperson Chris Caldwell pointed NBC News to an AP interview on March 1:
"U.S. Sen. John Boozman says he'll support Donald Trump in the November election if the billionaire and reality television star is the Republican presidential nominee."
Roy Blunt (MO)
"I'll support the nominee. I think any of our candidates would be a better president than Secretary Clinton or Senator Sanders."
Chuck Grassley (IA)
"I'm going to do everything I can to beat Hillary."
Johnny Isakson (GA)
"I support the ticket and I'm not endorsing anybody, and I'm not going to talk about it any further than that. I haven't endorsed anybody, and won't, and I'll support the ticket in November."
Mark Kirk (IL)
"The GOP nomination is a long and fluid process right now and we are not going to try to decrypt a very hazy and cloudy crystal ball," Kevin Artly, Kirk's spokesperson, said.
NBC5 Chicago's Mary Ann Ahern asked Kirk on camera if he would support Trump if he becomes the nominee. Kirk, who has not officially endorsed a candidate said, "If he's the nominee I certainly would."
John McCain (AZ)
Spokeswoman Rachael Dean told NBC News that the senator has "been very clear on this so I will let his previous statements stand."
When asked by NPR if he would support Trump, McCain repeatedly said "I said I'd support the nominee."
Rand Paul (KY)
"Senator Rand Paul will support the nominee," campaign spokesman Sergio Gor told NBC News.
Richard Shelby (AL)
"I haven't endorsed anybody, but I will support whoever is the nominee."
Senators unclear about Trump as nominee (6)
Kelly Ayotte (NH)
"Senator Ayotte intends to support the Republican nominee, however, she would like to see how the process plays out," spokesperson Liz Johnson and campaign spokesperson Chloe Rockow said in different statements.
Richard Burr (NC)
"I've always said I was going to support the nominee, I'm hopeful I'll be able to support the nominee."
John Hoeven (ND)
"My plan is to support the nominee of our party."
Ron Johnson (WI)
"Ron plans to support the Republican nominee for president. He has repeatedly said that he is praying for a nominee of integrity, intelligence, ideas, and courage who can lead our nation - not divide it," Brian Reisinger, Johnson's campaign spokesperson, said.
James Lankford (OK)
"It is the normal tradition of Senator Lankford to support the Republican nominee for President. However, this election cycle is very unique," campaign spokesperson DJ Jordan said. "Senator Lankford has concerns about Donald Trump and the vagueness of some of his policy decisions. But Lankford isn't getting involved in the Presidential election at all, right now."
John Thune (SD)
"Well, I intend to support the nominee. I've made that clear from the very beginning. And we don't know who that's going to be at this point."
No response (7)
Mike Crapo (ID)
Mike Lee (UT): Sen. Lee was the first senator to endorse colleague Ted Cruz.
Jerry Moran (KS)
Lisa Murkowski (AK)
Rob Portman (OH): Sen. Portman is currently backing Ohio Gov. John Kasich.
Tim Scott (SC): Sen. Scott previously endorsed colleague Marco Rubio before he dropped out of the presidential race.
Pat Toomey (PA): Sen. Toomey also backed Rubio before he suspended his campaign.
This article originally appeared on NBCNews.com.