AMNA NAWAZ: Stuart Stevens has spent the majority of his decades-long career getting Republicans elected to political office.

But his latest book is a warning to the country, not just about the current state of the GOP, but what he says is its threat to American democracy.

I spoke with Stuart earlier today about that book, "The Conspiracy to End America: Five Ways My Old Party Is Driving Our Democracy to Autocracy."

Stuart Stevens, welcome to the "NewsHour."

Thank you for joining us.

STUART STEVENS, Author, "The Conspiracy to End America: Five Ways My Old Party Is Driving Our Democracy to Autocracy": Thank you.

AMNA NAWAZ: So, in your book, you lay out five driving forces on the right that you say are working in concert basically to end our democracy.

You list them as propagandists, the support of a major party, financers, legal theories to legitimize actions and shock troops.

But I want to begin with this idea of support of a major party, because you draw a pretty alarming comparison.

In the book, you write: "What happened within the Republican Party in 2016 was a repeat of the rise of national socialism in the 1920s and 1930s in Germany."

You're arguing that the Republican establishment's acceptance of Mr. Trump echoed the German establishment's acceptance of Hitler.

What are the parallels you're talking about here?

STUART STEVENS: Yes, it's interesting.

For a long time, there was sort of a trope that any time you compared anything to 1930s Germany or World War II, it reduced it to sort of absurdity.

But I take a very different view, because I think the parallels are striking.

What happened in Germany was that the ruling class, mostly Prussian aristocrats, realized that they had lost touch with the working class, and they thought that they could control Hitler, that he would be someone who could connect them to the working class and take them into power.

And it's really exactly what happened with the Republican Party.

Mitch McConnell said that he was confident that Trump would change, that they would change Trump, that they were the mainstream conservative and Trump would adapt to that.

And it just proved to be incredibly naive, and it's still playing out.

And every chance the party has to turn against Trump, they go in the other direction, and they embrace him more.

AMNA NAWAZ: There are some along the way who've rung the alarm, so to speak, like Mitt Romney, for example, whose campaign you ran in 2012.

STUART STEVENS: Yes.

AMNA NAWAZ: He criticized Donald Trump, but then he considered joining his Cabinet.

So, you can't really argue that some folks didn't see the danger.

Is the story here that they just chose to ignore it?

STUART STEVENS: It's a fascinating question, because it is very difficult to find anyone in the Republican Party who will say in private that Donald Trump was a great leader, that Donald Trump is someone that they admire on any sort of personal level.

And yet they have basically turned over the party to him.

And I think that what happened here was that Donald Trump, in some sort of animal instinct, realized that the Republican Party ultimately did not believe in all the things that we had said that we believed.

What we said were values turned out to be marketing slogans, and that he realized that if he could give the party power, the party would go along with whatever he wanted.

And that literally is what's happened now.

And it's extraordinary.

I don't think we have seen anything like this in American history, just a complete collapse of a party.

But it's the reality.

It's the world that we live in, and it's not going to change.

He's probably going to be the nominee.

And there's a good chance he will be reelected president.

AMNA NAWAZ: You do talk about the impact of money in the chapter on the people who finance candidates like this, big money donors, who you say are complicit in helping to destroy democracy.

But why isn't there any kind of effort to get those big-money donors off the sidelines to coalesce around another candidate that could potentially beat Mr. Trump, if Republicans don't want him to be their candidate?

STUART STEVENS: Yes, I think this is a case in the primary where money is really not going to matter.

Tim Scott supposedly had backings of wealthy individuals who were going to put unlimited money in it.

And it really didn't matter.

There's not a market in the Republican Party of any size that is anti-Trump.

This is the thing that is difficult for a lot of us to grasp.

The Republican Party wants to be what Donald Trump has turned it into -- not turned it into, where Donald Trump has led it.

The party is what they -- there's nobody forcing them to support Donald Trump.

They don't have to.

They -- Trump has made it acceptable to embrace your worst self.

And once that becomes acceptable, it's very easy.

It's, I think, sort of addictive.

And now that's where the party is.

It's become a grievance party, and primarily a white grievance party.

AMNA NAWAZ: Stu, what about when you look at what's happening among House Republicans right now, their inability to elect a speaker?

Is that dysfunction at all related to any of this, or is that separate and apart?

STUART STEVENS: I think it's completely related to it.

At the core, there really is no governing principles to the Republican Party.

I mean, what does it mean to be an American conservative today?

I worked in the party for 30 years.

I have no idea.

And so, when you lack that ability to unite a party over a higher purpose, you end up in these sort of "Lord of the Flies" battles that they're in now.

So no one can stand up there and say to the Republican Caucus, look, it's really important that X-person be speaker because we have important business to do.

There's just nothing there that anybody can point to and say, this is what the Republican Party stands for with any credibility.

AMNA NAWAZ: Well, the book is "The Conspiracy to End America: Five Ways My Old Party Is Driving Our Democracy Towards Autocracy."

The author is Stuart Stevens.

Stu, thank you for joining us.

Good to talk to you.

STUART STEVENS: Thank you.