Conservative national security experts who vowed not to support Donald Trump are saying nothing has changed now that he is the presumptive nominee.

"When I said 'never Trump,' I meant it," Colin Dueck, an associate professor at George Mason University's School of Policy, Government and International Affairs, told the Washington Examiner.

Dueck was one of 121 conservative national security experts who signed an open letter in March promising to work "energetically to prevent the election of someone so utterly unfitted to the office."

The letter took issue with Trump's "wildly inconsistent" world views, his promise to reinstitute waterboarding and worse, his anti-Muslim rhetoric that alienates allies in the Islamic world, and his admiration for dictators like Russian President Vladimir Putin, among other things.

Dueck, who emphasized that he is speaking only for himself and not the other signatories, said no amount of foreign policy advisers can turn Trump into a candidate he could support.

"You could surround Donald Trump with 10 Henry Kissingers, and it wouldn't matter, because Trump does not have the personal qualities to be a good, serious commander in chief," he said. "That isn't going to change."

If the election in November comes down to a showdown between Trump and Democratic front-runner Hillary Clinton, Dueck said he'd vote for neither.

"If those are our only two choices this November, I'll write in the name of a conservative. Because otherwise there won't be one on the ballot," he said.

Bryan McGrath, a defense consultant who helped coordinate the open letter, told the Examiner that he will continue his push to make sure Trump doesn't win the presidency.

"I cannot vote for him," he said. "My approach is going to be that I will write in an actual Republican, not Donald Trump."

In speaking with other national security experts who signed onto the letter, McGrath said "virtually everyone" would pick Clinton over Trump in a hypothetical "gun held to your head" situation.

"If you look at domestic policies, they're both center-left politicians. If you look at foreign affairs, Trump is dangerous and unstable and Clinton is not," he said.

Some tell him they will vote that way, others say they will write someone in as he will, and still others say they won't vote at all.

Andrew Sagor, an associate at Paul Weiss law firm and former State Department official, said he is planning to vote for Clinton because, unlike Trump, she will garner respect among other world leaders and will not do things that put America in more danger.

"As a former Bush administration political appointee, lifelong Republican and a supporter of Jeb Bush's campaign, I never envisioned voting for Hillary, but I will do so and it will not be a difficult decision given the choice that is before us," he said.

A vote for Clinton will have more of an impact to keep Trump out of the White House than a write-in or vote for a third party candidate, Sagor said.

"While I would certainly support in principle a conservative write-in, both my principles and prudence dictates that I should vote in a manner that will have the greatest impact on Donald Trump's candidacy. And because I love my country, our Constitution and the freedoms our Constitution [have] helped to guarantee more than I do my party, I will vote for Hillary in November," he said.

Matthew Kroenig, an associate professor in the Department of Government and School of Foreign Service at Georgetown University, also said that Clinton is the better option.

"I vowed to work to stop Trump and, last time I checked, he is still utterly unfit for the office," he said. "I would warmly welcome the entry of a new candidate into the race. Short of that, Hillary Clinton is the strongest proponent of a conservative internationalist foreign policy left in the race."

Ken Adelman, a former ambassador to the United Nations and arms control director of President Ronald Reagan, said he will never advise Trump or vote for Trump, "no matter what."

"I hope Trump loses, and loses badly in order to teach the Republican Party, my party, a lesson in not allowing a totally unqualified man anywhere near the presidency," Adelman said. "I think it's a disgrace to the Party of Lincoln and of Reagan, and a real blight on Republicans. It's a real black mark on the nation."

Another of the letter's signers said he may end up voting for Gary Johnson, the libertarian candidate, "even though I am not a fan of libertarianism."

"I will happily support any credible third party or independent candidate who is better than Trump or Clinton — and that is a very low bar," said Paul Miller, associate director of the Clements Center at the University of Texas at Austin.

He wrote an article for The Federalist on Wednesday headlined "I am more qualified for president than Trump or Clinton, and so are you."

Miller said there are two better options: retired Gen. James Mattis, who has already said he will not run, and former Defense Secretary Robert Gates.

Carrie Cordero, an adjunct professor at Georgetown Law and another signatory of the letter who supported John Kasich, called the reported suspension of his campaign on Wednesday a "true disappointment for those Republicans who were seeking an alternative to Donald Trump's wild proposals and undignified campaign.

"Trump's rhetoric on national security and foreign policy, in particular, is uninformed and reckless," she said.

Cordero added that she does not and will not support Trump, whose foreign policy amounts to "promises without plans."

"His proposals to solve national security issues are like promises to win the national championship game, while leaving the team, the playbook and the ball in the locker room," she wrote in a Lawfare blog post published on Tuesday.

William Inboden, an associate professor at the University of Texas at Austin's LBJ School of of Public Affairs, said Trump's recent speeches only prove he is "fundamentally unfit to be our nation's commander in chief, diplomat in chief, and chief executive.

"I will not vote for Trump, nor will I vote for Hillary Clinton," he said. "But I will pray for my country."