Updated

The question of which party will control the U.S. Senate following the November elections could be decided by Susan Collins' bid for reelection in Maine, Fox News politics editor Chris Stirewalt said on this week's "I'll Tell You What" podcast.

Republicans currently hold 53 of the Senate's 100 seats, but are defending 23 of the 35 seats up for grabs in November.

"The races in Arizona [Martha McSally] and Colorado [Cory Gardner] don't look savable for Republicans right now, especially this late in the game," Stirewalt said, "but they are going to get one back in Alabama with [Democrat] Doug Jones [likely losing to Republican Tommy Tuberville].

DEMOCRATS RIDE 'GREEN WAVE' AS THEY TRY TO CAPTURE SENATE MAJORITY

"So they have to then, out of the three competitive races that are left -- Iowa, Maine and North Carolina -- the Republicans need to win two of the three to make sure that they hold the Senate," Stirewalt added. "If you're Mitch McConnell, you say, 'I got to win two of those three to make sure that I keep the Senate for the Republicans.'

Stirewalt said he was optimistic that Republican Joni Ernst would win a second term in Iowa, but was less certain about Thom Tillis' chances in North Carolina.

"I think he kind of screwed up his brand by going from pragmatic, conservative, Chamber of Commerce kind of guy to 'MAGA' guy," he said. "I think that may have hurt him in North Carolina a little bit. But Iowa's a much better state for Trump than North Carolina is, or we would expect it to be a better state for Trump than North Carolina is."

CLICK HERE TO GET THE FOX NEWS APP

If Stirewalt's instincts hold, he noted, "It's going to come down to ... Susan Collins' race is going to be astonishing. Can she hold on?"

Collins, who is the subject of a nationwide grassroots effort to unseat her following her vote to confirm Supreme Court Justice Brett Kavanaugh, is facing Democrat Sara Gideon in what the polls predict will be a close race.