Mitt Romney is ramping up his fight against Republican frontrunner Donald Trump by exploring ways to block the business mogul from securing the Republican party nomination, sources close to the 2012 GOP candidate told CNN Thursday afternoon.

via giphy.com

This is unprecedented in Modern American Politics.

Following his attack against Trump in a speech at University of Utah Thursday morning, Romney reportedly instructed his advisers to "explore the possibility of stopping Donald Trump at the Republican National Convention," CNN reports.

"It looks like the plan is to lock the convention," the source told CNN.

It's unclear what exactly this development will look like, but Romney, who called on voters to support the other 2016 Republican candidates on Thursday, is apparently hoping for a two-pronged plan to block Trump.

By pushing voters to support Ted Cruz, Marco Rubio, and John Kasich, Romney hopes to prevent Trump from getting the 1,237 pledged delegates needed to secure the party's nomination before the Republican convention in July.

In his speech, Romney said:

"Given the current delegate selection process ... I would vote for Marco Rubio in Florida, for John Kasich in Ohio, and for Ted Cruz or whichever one of the other two contenders has the best chance of beating Mr. Trump in a given state."

Then What?

Then the election would be taken out of the hands of so-called "pledged delegates," which are awarded to candidates throughout the primary process, and put into the hands of elected party representatives. In this scenario, these party reps would hand the nomination to Rubio, Cruz, or conceivably, Romney himself.

This would be the first Brokered Convention for the GOP since 1948.

After weeks of speculation, Romney's plan represents the first tangible effort by Republicans to achieve a "brokered convention," in which a party's candidate is decided mostly by backroom dealing and horse trading — far removed from the democratic process.

It also could drive Trump to abandon the Republican ticket and run as a third-party candidate — which could cause headaches for both Democrats and Republicans. Trump has signed a pledge to not launch an Independent run, but hinted he would break that pledged if treated poorly by the GOP. A brokered convention would certainly constitute poor treatment.

Earlier on Thursday, Romney warned that Trump's prospective nomination would "enable [Democratic presidential candidate Hillary Clinton's] victory."