ARI SHAPIRO, HOST:

Another primary day means another opportunity for the super PAC called Our Principles to try to slow Donald Trump's advance. Since January, Katie Packer has run the group, creating attack ads against the Republican frontrunner. She has worked in GOP campaigns for 25 years and joins us now in the studio. Welcome back.

KATIE PACKER: Thanks for having me, Ari.

SHAPIRO: Why did you decide this year, instead of working for a campaign, to work against a campaign?

PACKER: Well, I've been involved in Republican primary presidential campaigns for years and years and years, and I really was going to take this year off. And I didn't really expect Donald Trump to pick up steam. He was somebody that I thought everybody would recognize as kind of a phony and a fraud. And when that didn't happen, I felt like somebody had to do it. And I got together with some other people that agreed that this guy would be a problem for our party, that we would lose badly in the general election and that he would be terrible for our country. And so we decided to take action.

SHAPIRO: I want you to walk me through the chessboard. It seems like at this point, the most likely outcome that you would hope for is a contested convention where even if Donald Trump has more delegates than anyone else, he won't get an absolute majority, and someone would challenge him on a second vote. What happens if...

PACKER: Sure.

SHAPIRO: ...That is what you get?

PACKER: Well, just to be clear, you know, there's no talk of an actual brokered convention where party power brokers are trying to take over the process. This is the process. I was on Mitt Romney's campaign in 2012. We had to have 1,144 delegates to win the nomination. That day we got that, we had a big party in Boston because that's when you become the nominee. You don't get handed the nomination because you're doing well in a lot of polls. About a third of the delegates have been awarded. He, right now, has gathered about 40 percent of the delegates that have been awarded to date. Even from this point, to win 1,237 delegates, which is the magic number, he would have to win 54 percent of all of the remaining delegates, and he's not getting stronger. He's getting weaker.

SHAPIRO: But let's assume that he comes into the convention shy of that 1,237 magic number but with more delegates than anyone else. How do you tell the millions of Republican voters who have chosen him that even though your guy had more delegates than anyone else, at this contested convention, he's not the nominee?

PACKER: I would tell them that those are the rules. How do you tell these other candidates that those are the rules but then all of a sudden, they don't matter because somebody's in the lead even if they haven't won an outright majority?

SHAPIRO: This obviously points to a much deeper divide within the Republican Party. Some have referred to it as a civil war. What kind of work do you think needs to be done beyond this nomination fight to heal this kind of historic rift within the GOP?

PACKER: Well, I think that's something that the leadership is really going to have to take a long, hard look at, you know? What is it that's making the American people so frustrated that they would reach to somebody who's really just a con artist?

SHAPIRO: But if he's what you see as the symptom of the problem, how do you solve what you see is the underlying problem?

PACKER: Well, I don't know that I can solve that problem. I haven't been elected to anything. I'm just trying to inform people to give them the information they need before they cast a vote. But I do think that the people that are elected by, you know, the voters, you know, in both the primary stage and the general election stage really have to take a good, hard look. I mean, this is happening on the Democrat side as well - that people are very, very frustrated. They're taking those frustrations. They're showing up, aand they're basically telling Washington that they want to give them the finger, basically (laughter). And I think that's something that these officials in Washington need to take a good, hard look at. I just don't think the answer is electing a conman.

SHAPIRO: At this point, the likeliest alternative to Donald Trump appears to be Ted Cruz, who is not exactly beloved by Republican (laughter) leaders either.

PACKER: (Laughter).

SHAPIRO: If you prevent Donald Trump from being the nominee and Ted Cruz winds up being the nominee, are you going to feel like you've succeeded?

PACKER: Well, of course because Ted Cruz, John Kasich and Marco Rubio all have one thing in common. They're all conservative Republicans, and I think that is who should be our standard bearer. We're not advocating for a particular candidate. We just don't think that the Republican Party should be hijacked by somebody that, one, doesn't agree with our party on most core issues and, two, will lose miserably to Hillary Clinton in the fall because all of his rhetoric and his track record would unite the Obama coalition that was so successful against Republicans in the last two cycles.

SHAPIRO: Veteran Republican strategist Katie Packer is the founder of Our Principles PAC, formed to stop Donald Trump from winning the Republican presidential nomination. Thanks for coming in.

PACKER: Thanks for having me. Transcript provided by NPR, Copyright NPR.