We had planned to refrain from endorsing a candidate for president this year. But that was before Donald Trump became the Republican nominee.

We believe newspaper endorsements are valuable primarily because we can give readers the benefit of our access to candidates and issues on the state and local level. The more local the race, the more valuable, in our view.

We have no special knowledge about or access to presidential candidates, and what we do know is no more than any engaged voter can find out for themselves. Announcing our preference for one candidate over another isn't likely to persuade anyone, and we'll be guaranteed to anger, for no good reason, those who don't agree with us.

The 2016 presidential campaign, however, is like nothing we have ever seen and, we hope, unlike anything we will ever see again. We feel compelled to speak out because the stakes are too high. Donald Trump must not become president of the United States.

To prevent that unimaginable disaster, Hillary Clinton should be elected. We say that not because we are particularly enamored of the former secretary of state, U.S. senator and first lady, but because electing her will ensure that Trump is defeated — and because we believe she is prepared to do the job.

Trump, on the other hand, is utterly unfit to serve as president.

It's not his policy convictions that lead to that conclusion, because he apparently has none beyond what he thinks will sound good to his supporters on a given day. Trump has changed his position so often on so many things — NBC News documented 138 distinct policy shifts on 23 major issues since he declared his candidacy in June 2015 — that it's impossible to know exactly where he stands on anything.

On foreign policy, Trump is remarkably ignorant when he's not being frighteningly reckless. He has praised dictators for being strong leaders, suggested that China should invade North Korea, promised to "bomb the s--- out of ISIS" and "take their oil," threatened to withdraw support from NATO and from U.S. allies. He has said he knows more about ISIS than America's generals. Military and national security experts — some of them conservative Republicans — have denounced Trump as dangerous.

Trump has touted his success at business as a reason he would make a good president, but refuses to release his tax returns or reveal exactly how rich he is — or isn't. He has taken time off the campaign trail to visit resorts and hotels he owns, and has no real plan for managing his global businesses should he be elected, which raises huge potential conflicts of interest.

Trump is vindictive — lashing out impulsively against anyone who criticizes him in the manner of a spoiled child — and repeatedly threatens to sue people who accuse him of illegal or improper behavior, or who report such accusations. He has banned news organizations from his campaign events and suggested weakening libel laws to make it easier to squelch unfavorable coverage.

By comparison, Hillary Clinton is calm, measured and steady. Uninspiring on the campaign trail, she has not generated the kind of enthusiasm among voters that Barack Obama or her husband did. But she is undeniably prepared for the presidency, in stark contrast to her opponent.

Her policy positions include action on climate change, maintaining a strong military, providing health care for all Americans and supporting education. She calls for healing racial divisions and creating family-wage jobs. None of those is easy, and politicians always promise to make things better. But Clinton at least has concrete plans to accomplish them, while Trump just boasts that his plans will be "the best" without providing any details. His vow to repeal Obamacare and replace it with "something terrific" is a prime example.

Clinton would not be our first choice as a presidential candidate, but she is far from our last, and at this point, she's the only person standing between Trump and the White House. Voters should elect her. If you can't bring yourself to vote for Clinton, there are other choices. Just don't choose Trump.