Gov. Chris Christie got the debates exactly right.

"If you can't take it on the stage, no matter whether it's fair or unfair ... then how are you going to take running against Hillary Clinton?" he told NBC. "How are you going to take negotiating for America around the world?"

Being president is a pretty big job. Voters deserve to know how candidates react to adversity, perform under pressure, handle criticism and deal with crisis. And the debate stage is one of the few places in politics where those qualities are teased out and tested.

That's why the Republican candidates who keep whining about the unfairness of the last debate on CNBC badly misconstrue the role of an independent press.

Yes, some of the questions were too argumentative or disrespectful. Donald Trump might well be a "comic-book version" of a candidate, but those derogatory words went too far.

Many other questions were quite useful, however. Dr. Ben Carson will not tell you how much his tax-cutting plan will really cost the Treasury. It took a moderator to add up the numbers and point out that he would expand the federal deficit by $1.1 trillion.

Sen. Ted Cruz later said it was unfair to ask Carson, "Can you do math?" But isn't it rather important to know what a candidate's tax proposal will actually mean, especially if that candidate is now the front-runner? (Carson outpaces Trump in the latest Wall Street Journal/NBC poll, 29 percent to 23 percent.)

These candidates have countless opportunities every day to promote their policies and credentials, unchecked by media scrutiny. They have millions of dollars to buy TV and online ads that are carefully crafted to convey their precise messages.

They speak at rallies, issue statements, release videos. And they post comments on Twitter and Facebook that go directly to their supporters' tablets and smartphones, without any journalists getting in the way.

That's why debates are more important than ever. Sure, many of the answers are scripted, but still, the candidates are live on stage. Spontaneity happens. Some candidates seize the moment, like Marco Rubio; some get stung by it. Ask Jeb Bush.

There's a larger point here. Debates are a central part of the "media primary," the ongoing effort to investigate and interrogate the people running for the world's most powerful office. And while it's Republican orthodoxy to say the mainstream press favors Democrats, the facts tell a different story.

The Wall Street Journal, for example, counted up the cost of all the promises made by Sen. Bernie Sanders. The total came to $18 trillion, a fact all Democratic voters need to know before they cast a primary ballot.

Then there's the myth that journalists are soft on Hillary Clinton. In fact, Team Clinton constantly complains about its treatment by the mainstream media, especially The New York Times, which has doggedly pursued stories like the ones about the Clinton Foundation's finances.

Writing in Media Matters, a pro-Clinton website, Eric Boehlert charges that "the daily has been carrying around an unmistakable Clinton grudge for nearly 20 years."

By the way, remember who asked the toughest question of Trump in the first GOP debate: Megyn Kelly of Fox News. Hardly a Democratic partisan. To her credit, she was only doing what professional journalists are supposed to do: hold the powerful to account, in both parties.

That's the role that the Republican candidates refuse to recognize. Carson, for example, said on ABC's "This Week" that each candidate should be allowed "a substantial opening statement" -- in other words, a campaign commercial they don't have to pay for.

Asked what kind of moderators he would prefer, Carson replied, "moderators who are interested in disseminating the information about the candidates as opposed to, you know, 'gotcha,' 'you did this' and 'defend yourself on that.'"

But journalists are not there to spread the candidates' messages; candidates can do that for themselves. Their role is precisely what Carson denies and derides: to make politicians defend themselves and account for their past actions and positions.

Cruz was even blunter, saying any moderator of a GOP debate should be a Republican sympathizer. "How about instead of a bunch of attack journalists, we actually have real journalists," he suggested, like Sean Hannity and Rush Limbaugh.

Calling Hannity and Limbaugh "real journalists" is like calling Batman and Robin real people. But Cruz's ridiculous proposal demonstrates how right Christie is.

To paraphrase an old line often attributed to Harry Truman, "If you can't stand the heat, get off the stage."

Steve and Cokie Roberts can be contacted by email at stevecokie@gmail.com.

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