With Marco Rubio knocked out of the race and John Kasich barely surviving to fight another day, mainstream conservatives are redoubling their efforts to plot a course to prevent front-runner Donald Trump's coronation – or find an alternative. And fast.

The soul-searching in Georgia came even before Tuesday’s pivotal votes in five major states, which awarded the biggest delegate haul to Trump. His victory in Florida forced Rubio to suspend his campaign, though he couldn't hold off Kasich in his home state of Ohio.

Politico reports that Erick Erickson, the Georgia talk show host and outspoken Trump opponent, has joined with two other influential conservatives for a closed-door meeting on Thursday to explore running a "true conservative" challenger in the fall.

Donald Trump signed an oath to support the Republican nominee. I took no such oath. I will not support Donald Trump. Ever.

It is my hope that Donald Trump can be stopped. It is my hope Republicans will come to their senses. But the reality is that Trump is on a path to the nomination and, if not stopped, a viable alternative needs to stand up for those who refuse to vote for him.

Cruz's campaign is already focused on shadowy efforts to find unbound delegates for Trump who might be willing to leave him at the Republican National Convention. In Georgia, that effort begins in earnest on Saturday with grass-roots GOP county meetings across the state.

Others are increasingly worried about a permanent fracturing of the Republican Party as Trump consolidates the anti-establishment vote but struggles to win over mainstream conservatives.

Consider this from Seth Millican, a hardened Rubio supporter from Georgia who was despondent after his candidate bowed out:

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The Trump opponents are running out of time: He now has half the delegates he needs to secure the GOP nomination.

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