Inside the Last Ditch Effort for Republicans to Block Donald Trump

— -- With disapproval among the GOP mounting over Donald Trump’s controversial comments about the ethnicity of a federal judge, chatter is surfacing about ways to block the real estate mogul’s nomination at the convention in Cleveland this summer.

“I think the party ought to change the nominee, because we’re gonna get killed with this nominee,” said conservative radio host Hugh Hewitt. “They ought to get together and let the convention decide.”

Steve Deace, another conservative radio host, has also been calling on GOP convention delegates to revolt. And Illinois-based conservative radio host, Ian Bayne, has encouraged Trump-bound delegates and alternate delegates to simply skip the convention, potentially leaving Ted Cruz with a majority of bound delegates when a nominee is chosen.

According to the latest ABC News estimate, Trump has 1,543 delegates (including 127 superdelegates), putting him past the threshold of 1,237. Cruz has 561 delegates, including 11 superdelegates.

Pledged delegates to the GOP convention are bound to vote for a particular candidate on the first ballot but many are freed on the second ballot if a majority is not achieved, to choose whomever they want.

Since Trump has garnered enough delegates to clinch the nomination, according to RNC rules, the most feasible way for opponents to block Trump would be changing the number of delegates necessary for the nomination, and/or enabling delegates to unbind themselves without damaging the validity of their votes.

But such changes can only be made if they are approved by a majority of the convention's rules committee -- the 112 members responsible for drafting the rules of the convention -- and are only implemented if they are subsequently approved by the majority of delegates on the convention floor.

“I suppose you have to bet against it,” conservative commentator Bill Kristol, who is not a delegate, but has actively tried to recruit an independent candidate, told ABC News about the possibility of vanquishing Trump in Cleveland, “but I don’t think it’s nearly as out of the question as I would have thought a few days ago.”

Kendyl Unruh, a Colorado delegate and a member of the rules committee bound to Ted Cruz on the first ballot, told ABC News she intends to sponsor a “conscience clause,” enabling delegates to voluntarily unbind themselves based on their “personal or religious conscience” without penalty from the RNC.

“All I’m doing is adapting to the circumstances,” she said. “I certainly believe Trump’s demagogic racist comments are hurting him.”

Trump said that federal judge Gonzalo Curiel, who is American, but of Mexican descent, might be potentially biased in two lawsuits against his now-shuttered school, Trump University because of the real estate mogul's proposal to build a wall on the Mexican border. Trump has said that he is the "least racist person that you have ever met" and said that his comments about Curiel were "misconstrued."

The effort to block Trump is still in what Unruh called the “information gathering” stages. But she faces an uphill climb to convince fellow members of the rules committee that this is beneficial to the party.

The RNC declined to provide a list of the rules committee members. ABC News has identified 40, several of whom did not return phone calls. Those who did respond seemed reluctant or opposed to implementing a rule change as drastic as unbinding delegates.

“If she has a conscience problem, she should step down,” South Carolina delegate and rules committee member Cindy Costa said regarding Unruh’s proposal. “Donald Trump won it fair and square.”

Sandye Kading, a South Dakota delegate who is also on the rules committee, said the idea of unbinding delegates is unrealistic and would undermine the unity necessary to win the election.

Fellow South Dakota delegate and rules committee member David Wheeler said he would have “grave misgivings” about such a rules change, but it isn’t beyond the realm of possibility.

“The idea that the rules committee would make such a dramatic change is unlikely,” he said. “But this election has been unpredictable, so we can’t rule anything out.”