Bluffing is Donald Trump’s one great talent, and he brazenly bluffed his way to the Republican nomination. Now he is showing his cards, however, and they are utter garbage: racism, ignorance, capriciousness, egomania and general unfitness for office. That should be — it must be — a losing hand.

Imagine what a disaster it would be if this man were elected president. Really think about it. Then consider your obligation, as a citizen, to prevent such a thing from happening.

Mitt Romney is usually not the most eloquent of public figures, but he got it right when he explained his increasingly lonely resistance to Trump: “I wanted my grandkids to see that I simply couldn’t ignore what Mr. Trump was saying and doing, which revealed a character and temperament unfit for the leader of the free world.”

The outrages pile up so fast that it’s hard to keep track and put them in context. Trump’s reaction last week to seeing a black man at one of his rallies — “Look at my African American over here” — reflected a kind of casual bigotry. Much more sinister was his insistence that Indiana-born U.S. District Judge Gonzalo Curiel, who is hearing a civil suit against Trump University, is biased because “he’s a Mexican.”

Consider that for a moment. Trump’s argument, in essence, is that a judge of Hispanic origin should be disqualified from the case because Trump is so racist against Hispanics. Likewise, Trump claimed, a Muslim judge perhaps should be disqualified as well. He is basically saying that only Aryans need apply.

Republican presidential candidate Donald Trump told CBS's "Face the Nation" that the judge overseeing the Trump University case has treated him "very unfairly," and that "there is something going on" adding that he is biased. (Reuters)

Let me digress for a moment to recap what we know about “Trump University,” which I frame with quotation marks because the name is a total lie. As news organizations including The Post have explained, it was not a university at all but a series of seminars about investing in real estate. And, despite what was promised, Trump had little personal involvement beyond overseeing how the purported university was marketed to unsuspecting people.

The Post reported that one of the instructors’ central tasks was identifying which students had financial resources — then hectoring them to max out their credit cards or raid their retirement accounts to buy “packages” of additional seminars and counseling that cost up to $34,000. Some students believe they gained useful knowledge, but many believe they were hoodwinked.

Trump initially promised that any profits from the “university” would go to charity. Investigators estimate he made about $5 million before the operation was folded — amid a flurry of investigations and lawsuits — but not a penny went toward philanthropy. No one should be surprised. After all, Trump made a much-ballyhooed donation to veterans’ groups only after persistent reporters demanded to know where the money was.

I mention all of this because it speaks to Trump’s character, or lack thereof. If he were just a real estate developer and reality television star, the matter of the “university” would concern only Trump, his conscience and the relevant local, state and federal authorities. But next month, at what will surely be a bizarre convention in Cleveland, he will officially be named the Republican nominee for president. As such, his character is of urgent importance to the nation and the world.

GOP leaders who choose “party unity” over principle should know that there is no way back; when you embrace Trump, you make a decision that will stay with you forever. House Speaker Paul D. Ryan (Wis.), your claim to intellectual leadership of the Republican Party is forfeited by your endorsement of a man who mocks the high ideals you espouse. Senate Majority Leader Mitch McConnell (Ky.), your legacy is marred by support of a candidate you know to be unfit for the presidency. Sen. Marco Rubio (Fla.), your future in politics will be undermined by your support of a nominee you once rightly called a “con artist.”

I suspect that most of the establishment Republicans who now meekly support Trump believe he will lose, perhaps badly, and are positioning themselves for the aftermath. But that is no excuse for putting the nation in peril by endorsing Trump and thus bettering his chances, even incrementally.

He’s not going to change. He’s not going to become presidential, he’s not going to grow a thicker skin, he’s not going to take an interest in policy or become less of a bigot. He’s not going to temper his language or close his Twitter account. Donald Trump turns 70 next week. He is who he is.

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The question for those who cynically support him: Who are you?

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