A new 'Dump Trump' ad paints a stark comparison between Donald Trump and Ronald Reagan

A key group committed to thwarting Donald Trump's appointment as the Republican presidential nominee is set to air a TV ad aimed at GOP delegates ahead of the party's convention.

The group, Delegates Unbound, posted the ad titled "Follow Your Conscience" on YouTube. It juxtaposes unflattering clips of Trump next to decidedly more statesman-like snippets of former president Ronald Reagan.

At one point, Reagan is seen commenting on matters of war, saying "Use of force is always and only a last resort." Immediately after, a clip of Trump plays: "I would bomb the s___ out of 'em," referring to the Islamic State during an Iowa campaign rally in November.

The ad will be geared toward Fox and Fox News, The New York Times reported.

Delegates Unbound founder Eric O'Keefe told The Times, "Our goal is simple, to ensure the delegates are not misled to believe they must follow orders or rules set by others."

At least one Republican operative has called for an "insurrection" at the national convention, which kicks off in Cleveland on July 18. "I don't care what the rules are," Ted Cruz ally, Steve Lonegan said on CNN earlier this month, "Break the rules, unbind yourself," he said.

Trump has called efforts to push him aside "totally illegal."

Watch the "Follow Your Conscience" ad here: