Ted Cruz has described Tuesday's Indiana primary as "the one thing that stands between us and plunging over the cliff." The Texas senator and others trying to block Donald Trump from the Republican presidential nomination may be about to fall in. 

The outcome in Indiana, where balloting across two time zones will end at 7 p.m. Eastern time, could yield a deciding moment as the race enters the home stretch.

The voting comes as Republican establishment forces appear increasingly resigned to the likelihood of Trump as their nominee, while the ragtag coalition of donors and others that comprise the "stop Trump" movement is making what would seem to be its last stand.

Senator Ted Cruz speaks with supporters of Donald Trump demonstrating outside a campaign event in Marion, Indiana, on May 2, 2016.

Photographer: Luke Sharrett/Bloomberg

A Cruz loss could make the billionaire all but unstoppable in his quest to win the 1,237 delegates needed for the nomination, while a Trump defeat could rekindle the prospect of a contested Republican National Convention in July.

"The Cruz forces are the most well-organized in conventional political tactics, but in a year that defies convention at every step, the Trump phenomenon of mass rallies and digital media seem to have taken hold," said John Hammond, a Republican National Committee member from Indiana who has not endorsed a presidential candidate. "The demographic in the Hoosier State leans toward Trump."