Ann Coulter. Business Insider Conservative author Ann Coulter is such a fervent supporter of Donald Trump that she wrote a book, released this week, called "In Trump We Trust."

In the book, she wrote that there was only one thing the Republican nominee could do that would be unforgivable. And he already did it this week.

"There's nothing Trump can do that won't be forgiven," Coulter wrote. "Except change his immigration policies."

Over the past several days, Trump has moved to significantly moderate his hard-line immigration policies.

He has seemed to have abandoned his calls to deport the 11 million immigrants who are living in the US illegally, now suggesting that he wants to be "fair but firm" regarding illegal immigration. And though Trump said this week that he wouldn't support a path to citizenship, he did propose "back taxing" some of the millions of immigrants living in the US without permission, a step that would require some form of legalization.

"No citizenship," he said in a Wednesday interview with Fox News' Sean Hannity on Wednesday:

"Let me go a step further — they'll pay back taxes, they have to pay taxes, there's no amnesty, as such, there's no amnesty, but we work with them ... I meet thousands and thousands of people on this subject, and I've had very strong people come up to me, really great, great people come up to me, and they've said, 'Mr. Trump, I love you, but to take a person who's been here for 15 or 20 years and throw them and their family out, it's so tough, Mr. Trump.' I have it all the time! It's a very, very hard thing."

Coulter mocked Trump on Twitter after the Hannity interview for suggesting that it would be too hard to deport 11 million people:

Immigration has been a central issue in Trump's campaign, and his tough stance on the issue helped him secure the Republican nomination. He has faced criticism this week from some of those whose plans he attacked in the Republican primary campaign.