As concern grows about the repercussions of Donald Trump winning the GOP nomination, a trio of prominent conservative are planning to meet behind closed doors in Washington this Thursday, Politico reported, to discuss the possibility of backing an alternative to Trump. The meeting is schedule two days after Tuesday’s winner-take-all GOP primaries in Ohio and Florida, which are being treated as a do-or-die moment for blocking Trump’s path to the nomination.

According to the Politico report, those slated to attend include Republican figures with deep ties to the conservative movement: Erik Erickson, a conservative media activist; Bill Wichterman, a President George W. Bush aide; and Bob Fischer, a South Dakota businessman.

An invitation to the meeting obtained by Politico says participants will discuss “how to defeat Donald Trump for the Republican nomination” and “if he is the Republican nominee for president, to offer a true conservative candidate in the general election.”

New York Mayor Michael Bloomberg recently ruled out an independent run, having gone as far setting up field offices and cutting a rough version of a TV ad while considering running as an independent candidate.

Running an independent or third party presidential campaign is a costly and ambitious endeavor. Some states require thousands of signatures to get a candidate’s name on the ballot, and the deadlines are tight.