Conservative icon Richard Viguerie, the direct-mail fundraising pioneer who’s endorsing Sen. Ted Cruz for president, has a message for Donald Trump’s Tea Party supporters.

“If you are supporting Trump right now I would suggest that you reconsider based on this thought—‘Can you trust Donald Trump?’ ” Viguerie tells Breitbart News exclusively.

“He has spent his entire life walking with the establishment, walking with Big Government. He voted for Obama for President. He was proud of that at one point in time. He’s not somebody that you can be confident in and trust him to keep his commitments,” Viguerie adds.

On the other hand, “Ted Cruz is a man of his word. He’s demonstrated that he will bleed for conservatives. He will risk his political career. He’s done it over and over and over again. That’s one reason he’s not popular with a lot of Republican senators. Because he has a different world view. And he’s not popular for the right reason,” Viguerie notes.

Many of these Repubican senators are closer to Democrats in their world view than they are to grassroots Republicans. So if you’re considering voting for Trump, just take in consideration how confident can you be that he’s trust worthy and he will stay where he is now, because almost every position that he has now, he had a different position five or ten years ago.

While Viguerie asks Tea Party activists who are currently backing Donald Trump to reconsider that support, he also says that Ted Cruz is the only candidate for the GOP nomination who can keep them in the Republican fold if Trump does not secure the nomination.

“Ted Cruz checks all boxes for conservatives. It’s now time for conservatives who have been sitting on the sidelines to get off those sidelines and join the Cruz campaign,” Viguerie says.

Ted Cruz is the only movement conservative running, he’s the only limited government constitutional conservative Presidential candidate in the top tier. He’s the only candidate that walks with conservatives who’s in the top tier, therefore he’s the only candidate who unites all five parts of the Republican voting block. That’s Reagan’s three legs of the coalition: economic conservatives, cultural conservatives, national security conservatives, then since then we’ve added the Tea Party conservatives and then there’s the Libertarian voters out there.

“Of all the candidates running, Ted Cruz is the only one who can unite those five elements at the grassroots, and the Republican party must unite the grassroots,” Viguerie adds.

Viguerie says 2016 will be a base election. Cruz is the only candidate, in his view, who can turn out the base in ways the Republican party has not done since the Reagan era.

“If we don’t [nominate Ted Cruz and unite the base],” he warns, “we’re going to lose as we have consistently recently,” he notes.

“George H.W. Bush and George W. Bush did not unite the base of the party. The Republican party has been in violation of the Bible, as well as Lincoln’s advice—‘a house divided cannot stand,’” Viguerie says.

“Cruz is the only candidate who can unite the GOP. That is so important, because this will be a base election,” he adds.

“In 2012, Romney got 7 and a half percent more independent votes than Obama did. But Obama turned out his base, and the Republicans didn’t. Cruz is the only candidate who can do that,” Viguerie points out.

Viguerie says Cruz is the only candidate who can keep Trump’s supporters on board with the Republican party.

“Ted Cruz, of all the Republican candidates running for President, is the only candidate that can keep the Trump voters in the Republican party. It’s so important,” he notes.

“He’s the best candidate to keep Donald Trump himself in the GOP. They have a closer relationship, better relationship, those two, than Trump does with any other candidate,” Viguerie tells Breitbart News.

Viguerie credits Trump for bringing “Reagan Democrats” who left the GOP after the election of George H.W. Bush and his famously broken “read my lips, no new taxes” pledge, back into the party.

We must keep those Trump voters. Many of them are Reagan type Democrats who left the Republican party after Reagan left the White House and we have now the best chance to bring those people back into the Republican Party. If we nominate anybody other than Cruz and Trump does not get the nomination, I’m afraid those Trump voters will not turn out for the Republican candidate and Donald Trump could go third party.

Ted Cruz will push the evangelical and social conservative turnouts to historic levels, according to Viguerie.

If Ted Cruz is the nominee this election in 2015, we’re going to see a larger turnout of evangelicals and cultural conservatives than we have in American history. That alone is going to make an enormous difference when those evangelicals and cultural conservatives turn out for Ted Cruz, and they won’t turn out for any other candidate out there in the top tier right now.

In his endorsement statement, Viguerie highlighted Cruz’s personal qualities—his intellect, character, and personal discipline, as well as his commitment to limited government conservative principles.

Breitbart News asked Viguerie if his repeated use of the word “discipline” in his endorsement of Cruz was an implied criticism of Donald Trump, who some critics have described as “undisciplined.”

“I’m not so sure I would say an implied criticism, I think it’s more a direct criticism,” Viguerie tells Breitbart News.

“As somebody who is President of the United States, with the proverbial finger on the nuclear button, you need somebody who’s extremely disciplined, who we can have confidence in, is not going to fly off the handle, lose his temper,” he notes.

“Ted Cruz is a very measured, disciplined person who the American people will have a lot of confidence in that he is the type of person that not only do we want him in charge of our national security, but we want him as the person, rather than somebody who flies off the handle negotiating, sitting across from the world leaders,” Viguerie adds.

“You want somebody who’s very measured, thoughtful, and I think that’s Ted Cruz, unlike some of the other candidates running for President this year,” he concludes.

Viguerie says Cruz is the best candidate to debate and win against likely Democratic nominee Hillary Clinton across the board, but especially on foreign policy.

“This is an election where foreign policy will almost certainly play a major role. It may be the dominant issue in the campaign. If not it will be one of the top two or three issues,” he says.

“Foreign policy generally favors the Republican candidate. Ted Cruz is uniquely qualified to challenge Hillary on foreign policy in a way that no other candidate can,” Viguerie tells Breitbart News.

Viguerie’s endorsement was taken by many media outlets as an indication that momentum is moving toward Cruz in the race for the GOP nomination.

Though he still trails Trump by 19 points in the most recent national poll (The CBS-New York Times Poll has Trump at 35 percent, Cruz at 16 percent), Cruz appears to be establishing himself as the most viable alternative to the controversial and politically incorrect real estate billionaire from New York City. In Iowa, Cruz is in either first or second place in all the polls, and Politico recently declared him as the front runner.

Ted Cruz considers Viguerie’s endorsement so important he issued a press release publicly thanking him for his support.

With Iowa and New Hampshire less than two months away, reports that the Republican establishment is engaged in back room dealings to deny the nomination to either Trump or Cruz at the convention, and a growing consensus among Tea Party activists that Trump and Cruz are the only GOP candidates they are willing to support in the general election, Viguerie’s advice about what Republicans must do to win the White House in 2016 is resonating across the country among the conservative grassroots base of the party.