Donald Trump attacks journalists who dare to ask him hard questions. Now, according to Bloomberg News, he's urging his supporters to assail reporters who challenge him on a critical issue: his denunciation of a federal judge presiding over a fraud case against one of his business ventures, Trump University.

Trump says the judge, Gonzalo Curiel, cannot rule fairly because "he's a Mexican" and Trump wants to build a wall across the Southern border. "It's an absolute conflict of interest," he says.

Judge Curiel was born in Indiana, and many appalled Republicans agree with Speaker Paul Ryan that Trump's tirade fits the "the textbook definition of a racist comment." Trump now says his remarks were misconstrued, but that's absurd. Everyone knows what he meant. He even doubled down on his position, saying on CBS that a Muslim judge might also be prejudiced against him.

"The people asking the questions -- those are the racists," he said on a conference call, reports Bloomberg. "I would go at 'em."

We'll take that risk. We have two questions that bear directly on Trump's qualifications to be president, and voters deserve answers.

1. What don't you understand about the rule of law and the independence of the judiciary in the American system?

It's certainly fair to criticize judicial rulings; President Obama has done it many times. It's very different to question the qualifications of judges based on their ethnicity and race.

Newt Gingrich, who's been auditioning for the job of Trump's running mate, got it right when he told radio host John Gibson: "We don't judge you as part of a group. That would be to suggest that blacks can't get a fair white judge, whites can't get a fair black judge. Once you go down that road, you destroy America."

There's an even larger point here. Trump profoundly misunderstands the balance of power, and the role of the judiciary as a vital check on executive over-reach. His pugnacious attitude echoes the arrogance of Richard Nixon and the lawlessness that led to Watergate.

"This is how authoritarianism starts, with a president who does not respect the judiciary," writes retired law professor David Post. "The president has to be clear that the law is the law, and that he enforces the law. That is his constitutional obligation."

2. What don't you understand about the history of this country and what it means to be an American?

Judge Curiel is a classic immigrant story. His father worked as a farm laborer in Arizona, became a steelworker in East Chicago, Indiana, sent his son to law school and saw him become a federal judge in California.

The Curiels represent this country's highest ideals. The judge achieved his position based on merit, not birth. He is fully an American, and if Donald Trump doesn't understand that, he doesn't grasp the essence of the nation he seeks to lead.

Even Sen. Mitch McConnell, the Republican leader who has jumped on the Trump train, could not stomach his latest lunacy. McConnell's wife, Elaine Chao, was born in Taiwan and became Secretary of Labor, so he speaks from experience.

"All of us came here from somewhere else," he told NBC's "Meet the Press." "Almost all Americans are either near-term immigrants like my wife, who came here at age 8 not speaking a word of English, or the rest of us whose ancestors were risk-takers who came here and made this country great. That's an important part of what makes America work."

Often during the last year, Trump has made what would seem to be fatal political mistakes: demeaning John McCain's prisoner of war experience, for example, or endorsing punishment for women seeking abortions. He survived them all, but this controversy could be different.

America is changing very rapidly, and the electorate will be only 70 percent white next fall. Trump now has to appeal to all voters, not just older white male Republicans, and he's alienating, yet again, the fastest-growing group in the country.

"It's a big mistake for our party to write off Latino Americans," noted McConnell, adding that "they're an important part of the country."

More seriously, Trump's conduct reveals a streak of intolerance and intemperance that many voters could find deeply disturbing. And it is those voters, not journalists, who will ask the most important question of all: Does this man have the judgment and character to be president? Can we trust him to keep our families and our country safe?

If the Curiel case is any guide, the answer should be "no."