Politico predicts the battle for the GOP nomination may come down to two sitting senators:

Going into the week, Jeb Bush and Marco Rubio seemed to be the rivalry to watch in the GOP primary. After the fourth Republican debate, that’s been replaced by a new and perhaps more consequential storyline: the coming collision of Rubio and Ted Cruz.

The two Cuban-Americans, both 40-something, first-term senators with tea party credentials, continue to trail outsider candidates Donald Trump and Ben Carson in the polls. But they’re increasingly viewed as the candidates to beat in their respective lanes — Rubio as the new establishment front-runner and Cruz beginning to consolidate support from the party’s more conservative wing. The consensus view that they outperformed their rivals Tuesday has served only to cement that impression.

“There’s this growing sense that Rubio’s the best candidate and that people are getting pretty comfortable with him,” said Bruce Haynes, a Republican strategist. “You can feel Carson and Trump losing support. Cruz is a quiet tide in the night that is beginning to wash out the base on Donald Trump. Now, I think, people are looking at Cruz as the candidate who’s best positioned in a lane to run with Rubio and give him a real fight.”