“No man is good enough to be president,” wisely observed Abraham Lincoln, one of the nation’s greatest, “but someone has to be.”

Americans’ choice of a president is truly the most personal vote that any of us will ever cast. We are far more likely to vote strictly on issues — whether taxes, education or the environment — when choosing our representative in Congress or the Senate. But the higher the office, the more important the candidate.

We want to know of a presidential candidate not simply the voting record or the position papers, but instead what kind of a person, parent, spouse, friend, colleague, ally or adversary the nominee really is. Generally, before we vote for somebody, we have to first like that somebody.

The American presidency is the center of American political power. A president can do for the nation and for the future great good or great harm — and, sometimes, both. Presidential elections really do matter. Just ask any African-American who was drafted into the U.S. military after President Harry Truman signed Executive Order 9981 in 1948, which began the desegregation of the armed forces.

The presidential election of 2012 demands a serious public debate about what kind of country we want our children to live in, about what we want the federal government to do — and not to do — and about who should pay for it. Every presidential re-election campaign is, by definition, a referendum on the incumbent president’s record. When three out of four citizens believe that the country is “seriously off on the wrong track,” the incumbent’s record ought to be fully, freely and honestly criticized and debated in the campaign.

That will not happen in 2012 if the Republican Party nominates former House Speaker Newt Gingrich, R-Ga., for president. There would be no urgently needed debate about what went right and what went wrong in President Barack Obama’s first term or what changes must be made, whether Obama wins re-election or he doesn’t.

Why? Because if Gingrich is the Republican nominee, the campaign will be all about Gingrich and his manifest shortcomings — political, public and personal. Americans like their presidents to have both confidence and modesty. Forget that Gingrich has in the past compared himself favorably to Charles de Gaulle, Margaret Thatcher and former President Ronald Reagan.

Last week, in The Right Fights Back, a new e-book by two outstanding journalists, Mike Allen and Evan Thomas, Gingrich spoke of his unflagging confidence even as his own 2012 campaign cratered last summer: “I told somebody at one point, ‘This is like watching (Sam) Walton or (Ray) Kroc develop Walmart and McDonald’s.”

Of his current and third wife, Callista, Gingrich told ABC News last week, after comparing her earlier to Nancy Reagan in the Allen-Thomas book, that “she (Mrs. Gingrich) actually describes herself as being a cross between Nancy Reagan and Laura Bush, with just a slight bit of Jackie Kennedy tossed in …”

Forget that Gingrich is the only House speaker in U.S. history to be disciplined by his House colleagues in both parties for violating tax rules and to be fined $300,000. Forget that he has more skeletons in his closet than does the lab at Harvard Medical School.

If Gingrich is nominated, there will be no debate and, consequently, no accountability for the Obama stewardship. The race will be all about Gingrich, and Gingrich will be rejected overwhelmingly by the voters. We will not debate or decide what we need to do, what sacrifices we must all make, what pain we must endure for the common good. Obama will never be held accountable. He will get a free ride to a second term, and the nation will resolve nothing.

This is a plea to my Republican friends and relatives: For your own sake and for the good of the country, please do not nominate Newt Gingrich.

Mark Shields is one of the most widely recognized political commentators in the United States. The former Washington Post editorial columnist appears regularly on CNN, on public television and on radio. Click here to contact him.