It was once unimaginable. Now Donald J. Trump – the reality TV star, questionable businessman, and political bomb thrower – is on the verge of becoming a major party’s presidential candidate.

When Mr. Trump ran for president on the Reform Party ticket in 2000, his candidacy was scoffed at. He was an unserious man running for the most serious position in the free world, and everyone knew it.

Yet now, many Americans – from the public, to the media, to politicians in Washington, D.C. – seem to be acquiescing to the idea of a Donald Trump candidacy and presidency.

The entire country seems to be falling down the rabbit hole.

Donald Trump is unfit to be president of the United States for reasons almost too numerous to mention.

First, Donald Trump’s sole motivation for seeking the presidency is Donald Trump. His careers in business, reality television, and politics have been marked by personal ambition, self-aggrandizement, and a willingness to do or say anything to achieve power, fame, or notoriety. He is exactly the kind of demagogue that our founders feared might try to seek the Presidency for his own personal gain.

Furthermore, Trump lacks the judgment, character, and emotional stability to be president. Given his frequent public outbursts and lack of self-restraint, the thought of Mr. Trump controlling our military and nuclear weapons is unacceptable. The GOP, which has spent decades claiming to be the party of national security, should have been the first to declare Trump unfit for the presidency.

Instead, the opposite has happened. As Trump moves closer to the GOP nomination, many Republican leaders in Washington and across the country have begun to embrace him. Most have not done so because they truly believe in Mr. Trump, but because they have been blinded by personal ambition, ideology, and partisan politics.

Some opportunistic politicians, like Governors Chris Christie and Paul LePage, endorsed Mr. Trump early on in the hopes of future personal benefit. (Mr. LePage, for example, privately proposed that the GOP disavow Mr. Trump on February 20. Six days later, he endorsed him. What else could explain that change besides pure political calculation?)

Worse still are those Republicans who privately (or publicly) oppose Mr. Trump, yet will support him as the Party’s nominee.

From 2006 to 2009, I worked in the White House for George W. Bush. As an actor and writer in New York, this isn’t always a popular thing to tell people. But I do, because I am proud to have worked for a president who led with principle and conviction. As a West Wing staffer, I saw firsthand that President Bush’s sole motivation was to do what he thought was best for our country. People may have disagreed with his policies, but they couldn’t disagree with his intentions.

From 2009 to 2010, I spent a year working for Congressional Republicans. In contrast to my time at the White House, I saw that many in Congress put their personal and partisan interests ahead of the country’s needs. Many times, the GOP’s only agenda was to defeat Barack Obama at all costs. It didn’t matter what Obama’s policy was; all that mattered was winning and eventually regaining power for the GOP.

This desire for control of the presidency, and the belief that any Republican is better than any Democrat, is why many Republicans are now embracing Trump. They claim that the GOP needs to coalesce behind Mr. Trump because he is a better alternative than Hillary Clinton. He is not.

To begin with, Mr. Trump has autocratic tendencies, and openly admires tyrants such as Vladimir Putin. In fact, his narcissism and cult of personality leadership style seem better suited to countries like North Korea and Uzbekistan than America. Trump has repeatedly attacked core conservative principles such as freedom of speech, freedom of religion, and American leadership on the world stage. He has incited the use of violence against his detractors, called on America to commit war crimes, and suggested the possibility of civil unrest if he is denied the GOP nomination.

Mr. Trump proclaims that he’s going to make America great again, but can’t provide any realistic plans for doing so; instead, he frequently resorts to scapegoating outsiders, foreigners, and minorities. The few policies that Trump has articulated would make America less safe, trample upon our most fundamental rights, and appeal to the basest instincts of the American people.

While I disagree with many of Hillary Clinton’s policies, she is clearly qualified to be president. She possesses judgment and self-restraint. She does not have a track record of irrational, risky, and unsound business decisions and public comments. She has a long record of public service. She can be trusted with controlling our military and nuclear weapons. Mr. Trump cannot.

Any Republican who claims that it’s better to elect Donald Trump than Hillary Clinton either lacks proper judgment, or has become so blinded by partisan ideology that they have lost objectivity.

Many of the GOP voters who support Trump are backing his candidacy because they are desperate for change in Washington. But Republican leaders who embrace Trump aren’t hearing the public’s message or embracing change. Instead, they’re doing what they have always done: whatever is necessary to gain or retain political power.

I saw the same thing happen during my time in Washington with the rise of the Tea Party. Instead of adopting the movement’s more valid positions, such as a real crackdown on Wall Street and corporate America, many Republicans jumped on the bandwagon of hate and divisive rhetoric because they thought it was their best chance of being re-elected.

Yes, Mr. Trump has populist support. But a true leader doesn’t jump on the populist bandwagon – especially when that bandwagon threatens to irretrievably harm their country and party. A true leader explains why that candidate cannot and should not be trusted, and is willing to suffer any consequences that might result from standing strongly behind their position.

Alexander Hamilton has become a cultural zeitgeist recently due to the success of the Broadway musical about his life. Yet Americans are responding to more than a brilliant piece of theatre. They are responding to a time of great men and women in American history -- true leaders who put their love of country above their personal ambitions or partisan ideologies.

In fact, Hamilton faced a choice similar to the one Republicans are facing today. During the election of 1800, Hamilton had to choose between endorsing Thomas Jefferson, his life-long political rival with whom he disagreed on almost every major issue – or Aaron Burr, a dishonest man of flawed character, who many feared would lead America down a dangerous path of tyranny and oppression. Mr. Hamilton chose to endorse Jefferson.

There is still time to stop Donald Trump from becoming the GOP nominee. Republicans must speak out loudly and forcefully against his candidacy – and they must oppose Trump even if he becomes the party’s nominee.

The United States of America was built on 240 years of blood, toil, and sacrifice. We owe our ancestors, and our children, so much better than handing this country over to a man of Mr. Trump’s character and intentions.

Voters will not forget those individuals who supported Mr. Trump. And any Republican who endangers our nation by supporting Donald Trump will not be trusted again.

David Meyers worked in the West Wing of the White House as Assistant Staff Secretary from 2006 to 2009 and Communications Project Director. From 2009 to 2010, he worked as a Communications Advisor for the Senate Republican Leadership. He is now an actor, writer, and Ph.D. candidate in Political Science.