AMNA NAWAZ: Still a year to go before Election Day 2024, and the Republican presidential field continues to shrink.

So far, polls have shown that former President Trump continues to lead the field and could likely be the party's nominee to challenge President Joe Biden.

Jonathan Karl is ABC's chief Washington correspondent and the author of "Tired of Winning: Donald Trump and the End of the Grand Old Party."

Jon joins me now.

Jon Karl, welcome to the "NewsHour."

Thanks for joining us.

JONATHAN KARL, Author, "Tired of Winning: Donald Trump and the End of the Grand Old Party": Thanks for having me, Amna.

AMNA NAWAZ: So, you write that Trump today has remade the party in his own image.

What does that mean?

What are the key ways the party is different today than it was, say, back in 2015?

JONATHAN KARL: The party is largely driven around him, his personality, the image of Trump as the guy that is the ultimate winner, the image that he's cultivated for himself.

Policy seemed to have receded into the background.

I mean, there are a few broad brushstrokes on things like immigration, tariffs, largely a more isolationist approach to the world.

It's very different on those policies from the party of Reagan and McCain and Bush and Romney.

It's a very, very different party.

In fact, most of those figures, certainly the Bushes, Romney, Jon McCain before his death, had essentially been banished from the party once Trump came in.

I think it's a very different party.

AMNA NAWAZ: And when you look at just some of the events we have seen among Republican lawmakers in the last few weeks, right, there was the chaos of electing a new speaker in the House.

There was an alleged shove between the former speaker and one of the people who voted to oust him, a sitting senator threatening to fight a hearing witness.

Are all of these sort of characteristics in that new party in the image of Trump?

JONATHAN KARL: I mean, it's toughness, it's brashness, it's image over substance, I think a lot of that, for sure.

And it's interesting with -- McCarthy is one of the people that helped Donald Trump come back.

He left the White House in 2021 in disgrace.

He was a defeated president, an impeached president, a president that was facing all but certain legal criminal prosecutions.

And Kevin McCarthy went down to visit him eight days after he left the White House.

I think, largely, the calculus, he wanted to get Trump's support, at least not have Trump working against him, so he could become speaker of the House.

But it followed the pattern.

So many people who have come into contact with Trump, whether it's his opponents or his allies, or people who have worked for him, have had their lives turned upside down.

Kevin McCarthy did get elected speaker.

It wasn't easy.

And then he got unceremoniously pushed aside.

AMNA NAWAZ: Jon, the party had chances to break with President Trump.

We thought January 6 might be one of those dates.

And you include this remarkable photo from right after Vice President Pence was evacuated.

His wife is literally closing curtains in their new secure room to try to hide them from view as protesters outside are chanting, "Hang Mike Pence."

When you ask Mr. Trump about that a few months later, he makes excuses for that.

He defends those people.

And you write this in the book: "I figured these words would surely be the last straw, driving top Republicans to finally disavow the leader of their party once and for all."

But that is not what happened.

Why not?

JONATHAN KARL: Well, and the specific quote from back then that I thought was so incredibly damning is that he was defending the people that were calling for Pence's execution.

He was saying, well, they were angry.

And then he went further to say that, how could you pass on a fraudulent vote?

In other words, making the argument, making the case for those that were arguing -- chanting, "Hang Mike Pence."

To this day, he has never criticized those chants.

He has never said anything remotely critical about that, about that whole effort.

And, in my interview, he was justifying it.

Look, I think that what happened is two very critical moments, one, as I mentioned, McCarthy going to see him just after he left the White House.

The other, though, was Ronna McDaniel.

Trump threatened -- the day that he left the White House on January 20, 2021, he threatened to leave the Republican Party and start his own party.

And Ronna McDaniel, like, begged him to stay in.

And then when that didn't work, she threatened him.

Her and the leadership of the RNC made it clear they were going to stop paying his legal bills and they were going to make it virtually impossible for him to raise money the way he had been raising money using their mailing list.

And Trump relented and he stayed in the party.

I mean, what if McCarthy had said, good riddance, we're not -- I'm not going to go back there and kiss the ring again, I'm not going to -- Trump's gone, we have to move forward?

What if Ronna McDaniel said, go ahead, try it, try to make your own party?

At that point, he was disgraced.

His popularity was at an all-time low.

And they instead felt that they needed to bring him in, to keep him in, because, if he left, the hardcore supporters, even if it wasn't a majority of the party at that point, would leave, and they would have a hard time winning.

Well, guess what?

He stayed, and then they went and lost over and over and over again.

AMNA NAWAZ: Jon, this is your third book about Trump.

And after the second one, "Betrayal," you said you felt a degree of optimism as you finished it, because, at the time, Mr. Trump and others' efforts to overturn the election didn't work and the system held.

How do you feel now going into 2024?

JONATHAN KARL: Well, I think it's an ominous time.

This is actually a different Trump.

Many of the characteristics are the same, but he is far more willing even than he was on January 6, I think, to trash the norms of American democracy, the things that make American democracy work.

And he has many fewer restraints, virtually no restraints, because, on January 6, my optimism was based on the fact that there were good people around him, people who supported him who refused to do his will at the end when he tried to break the system.

Well, those people are gone now.

I'm still optimistic by nature.

I look at the way voters rejected in the midterm elections the efforts to -- the lies about the election being stolen.

So, I'm still ultimately optimistic about all of this.

But the bottom line is, the people that stood up to him have been exiled from the Republican Party, and this is going to be a tough battle.

AMNA NAWAZ: Jon Karl is the chief Washington correspondent for ABC News and the author of the new book "Tired of Winning: Donald Trump and the End of the Grand Old Party."

Jon, thank you.

Good to talk to you.

JONATHAN KARL: Thank you, Amna.