One of the most vulnerable U.S. senators in next year’s election is Republican Thom Tillis of North Carolina.

Tillis has gained a reputation in recent years as a moderate Republican.

So, when the Senate began taking up President Donald Trump’s cabinet picks, the thought was he might oppose some of the more controversial nominees.

So far, he’s voted for all of them.

“I mean I think Tillis was pretty clear on this from the beginning ... Tillis was unsure on some of these folks ahead of time, but once it made it out of committee, once it made it to the floor he was going to fall in line. And he did fall in line,” Western Carolina University politics Professor Chris Cooper said.

A few Republican senators, including Lisa Murkowski and Mitch McConnell, did vote against a few of Trump’s nominees. And The Wall Street Journal reported that Tillis would join them in voting against Pete Hegseth for defense secretary. But he ended up voting for Hegseth.

Tillis has delivered impassioned speeches opposing the president’s pardon of January 6 rioters who hurt police officers and voicing more support of Ukraine than the president showed. But he has sided with the White House on many other issues.

“Cash on the barrel head. If you look at who gives money to incumbent politicians it tends to be the folks from either extreme,” Cooper said. “It’s of course about winning the primary, but it’s also about winning the general and having enough to win the general.”

Cooper said it’s a reflection of Tillis’ tricky balancing act in his re-election campaign.

“Every day as we get closer to the election, the tight rope gets harder and harder and harder to walk,” Cooper said. “He’s going to get hit by one side or the other almost no matter what he chooses to do.”“Every day as we get closer to the election, the tight rope gets harder and harder and harder to walk,” Cooper said. “He’s going to get hit by one side or the other almost no matter what he chooses to do.”

Although a few Republicans have jumped in to run against Tillis in the GOP primary, no big-name Republican has done so yet.

He’s helped by the lack of prominent Republicans in the state who are fitted for a major challenge. Cooper said when you look at the state’s congressional delegation there aren’t any obvious choices given many are established in their positions or too new to Washington to mount a noteworthy challenge.

It’s also been more than 10 years since an elected, sitting senator lost a primary.

But it’s the general election in November next year that’s a much more challenging path.

“He is absolutely one of the most vulnerable senators next year,” Cooper said.

That’s because of the Republican Senate seats up for election next year, North Carolina has significant potential to flip it. Maine, which is represented by Republican Sen. Susan Collins, is another to watch.

Former North Carolina congressman Wiley Nickel has expressed interest in running against Tillis, but the big wild card is whether former North Carolina Democratic Gov. Roy Cooper enters the race.

“If it’s Roy Cooper who gets in on the Democratic side it’s going to be a barn burner,” Chris Cooper said. “I don’t know who’s going to win, but it’s going to be incredibly close.”