David M Jackson

USA TODAY

HOUSTON — Marco Rubio and Ted Cruz are ratcheting up their attacks on Republican front-runner Donald Trump, but many political professionals wonder whether it's too late.

At this point, analysts said, odds are the race for the GOP nomination has only two outcomes: Either Trump secures a majority, or there will be a contested convention.

"That’s our conclusion after doing some back-of-envelope math looking ahead to Super Tuesday and the winner-take-all March 15 contests," NBC News reported.

The New York Times notes that Marco Rubio could challenge Trump in delegate numbers, even if he loses every state in Tuesday's contests but finishes high enough.

Cruz, who is tied with Rubio for second in delegates according to some estimates, could get back in the game with wins in his home base of Texas and other Southern states on Tuesday.

That window closes, however, on March 15 — the day that winner-take-all contests start.

"If Mr. Rubio can’t hold his own in those states — Illinois, Ohio, Florida, Missouri and North Carolina — it will become extremely difficult for him to finish the primary season with a lead in pledged delegates," the Times reports. "His more realistic strategy then would be to deny Mr. Trump a majority and hope to win at a contested convention."

NBC drills down more into the numbers here.