As they try to derail Donald Trump, Texas Sen. Ted Cruz, Florida Sen. Marco Rubio and Ohio Gov. John Kasich are facing enormous pressure in their home state primaries.

Donald Trump and Ted Cruz participate in the Republican presidential debate at St. Anselm College in Manchester, New Hampshire. (Photo by Joe Raedle/Getty Images)

The Texas, Florida, and Ohio primaries account for about a fourth of the delegates up for grabs in the next three weeks.

Failure to defend their turfs could leave each explaining what states they 'can' win.

The presidential race now shifts to Super Tuesday, featuring 11 largely southern states, including Texas, whose 155 GOP delegates are the top prize.

Then, on March 15, Florida's 99 delegates and 66 Ohio delegates are at stake.

If no one can dent Trump's advantage by then, the race may be all but over.