The 30-second TV ad is scheduled to air Sunday, Monday and Tuesday on the Fox News Channel -- an outlet popular with Republicans -- during national ad breaks, according to Dane Waters, one of the leaders of Delegates Unbound. His group has been fighting for years to ensure that GOP delegates can vote however they want during a nominating convention instead of being bound to the results of state caucuses and primaries.
The group is now spending money on advertising in hopes that Republicans upset by Trump's campaign and interested in finding ways to nominate someone else will see the ad and urge delegates from their state to support changes to the convention rules that would block Trump from the nomination.
“Our goal is simple, to ensure the delegates are not misled to believe they must follow orders or rules set by others,” Eric O’Keefe, a founder of Delegates Unbound, said in a statement.
The group is comprised mostly of longtime GOP operatives. They've joined up in recent weeks with an upstart group, Free the Delegates, that is working to codify convention rules allowing delegates to vote their consciences. Another organization, Courageous Conservatives PAC -- that spent money in support of Texas Sen. Ted Cruz's failed GOP presidential campaign -- is helping bankroll a national outreach campaign.
Kendal Unruh, co-founder of Free the Delegates, said her group is happy to have others spreading the word on a wide scale while she focuses on wooing other delegates to her cause. The three entities finalized their new approach during a conference call on Friday.
The ad campaign is "the top-down approach," she said in an interview after the call. "I’m not the top-down approach kind of person, I’ve always been a grassroots kind of person. But when the top-down and the grassroots meet, you have a complete, 100 percent effective plan. And we need that plan in order to combat Trump, who’s now waking up and realizing we’re not a hoax."
Trump has dismissed talk of using convention rules changes to stop him as an illegal tactic. His campaign announced plans this week to use a mix of 150 campaign staffers and volunteers to stop delegates from voting against him at the Cleveland convention. Details of the plan were shared with Trump-supporting lawmakers during a meeting this week in Washington.
Unruh said her group isn't worried by Trump's sudden interest in their attempts to stop him.
"He’s relying on campaign funds that he should have been spending against Hillary [Clinton], not delegates in his own party," she said. "Usually a campaign has enough volunteers that you can rely on to do your bidding at a convention."
Sean Sullivan contributed to this report.