He has run for the Senate, for governor and, twice, for president. He has given more campaign speeches in high-visibility circumstances than almost anyone in the country. And still, after 18 years on public rostrums and in the public eye, he remains the most mysterious figure on the American scene.

On the surface, he may seem the least likely politician of the age to be regarded as mysterious at all — but the plain talking, seldom excitable and rarely exciting Mitt Romney, who has been speaking four or five times a day for more than a year, has revealed almost nothing about himself and his views.

Indeed, Romney is, as Franz Liszt said of Frederic Chopin, “prepared to give anything, but never gave himself.”

America has had political figures with a mania for privacy before; Calvin Coolidge gave up little about himself, and the two President Bushes were so reluctant to share their personal thoughts they disparaged even the idea of introspection, saying they didn’t want to sit in a psychiatrist’s chair.

Not all privacy-preserving politicians are Republicans; both former Vice President Walter F. Mondale and former Gov. Michael S. Dukakis of Massachusetts failed to win the White House in part because they didn’t share the warm, engaging sides most voters still don’t believe they possess.

Man of the future?

But seldom has a major American political figure so hidden both himself and his own ideas as Romney, who, like most politicians, prides himself as a man of the future rather than the past and, like almost all successful leaders, argues he is not a prisoner of the past. He is not, as John Maynard Keynes might say, the slave of “some long-dead economist” — not that Romney himself would be caught dead quoting Keynes.

Political polls have shown remarkably little movement in recent months, with President Barack Obama holding a steady but slim lead over Romney. While it is impossible to isolate a single reason why a business-oriented Republican has failed to overtake a regulation-oriented Democrat at a time of stubborn economic distress, it remains remarkable that Romney has proffered so few new ideas of his own.

This is not to say that Romney is running an empty, media-oriented campaign. He has plenty to say, about economics, gay marriage and, after his overseas trip, about national security and diplomatic matters.

But except perhaps for his China policy, his proposals, dutiful and detailed, are more derivative than innovative or original. They are a quilt of notions about the size of government that can be traced to Ronald Reagan; views about social issues with strong roots in religious conservatism; assertions of American exceptionalism growing out of the neoconservative wing of the Republican Party; and expressions of impatience with the status quo ripped from the labels of the tea bags on the muscular right of the conservative movement.

Everyone’s not an original

Not all American politicians are American originals, of course. Gov. Franklin D. Roosevelt had very few ideas when he ran for president in 1932, and even from this distance it is difficult to distill a consistent ethic from the New Deal except for the determination to do something, and then to do something else, until something worked or until the Supreme Court struck it down.

Only in the White House did Lyndon B. Johnson, a conventional New Dealer but mostly a wheeler-dealer, make the full transformation from Senate institutionalist to presidential idealist.

But some candidates, like Sen. Gary Hart (1984 and 1988) and Rep. Jack F. Kemp (1988), are founts of new ideas. Sen. John F. Kennedy (1960) and former Gov. Reagan (1976, 1980 and 1984) ran on very big ideas, with oversized rhetoric to match — rhetoric that, in both cases, stirs Americans still.

Wizardly manager

For his part, Romney is running as an exceptionally gifted, almost wizardly manager armed with conventional conservative ideas, though Americans rarely elect managers, who in folklore, if not in reality, often have the political sex appeal of accountants. The only exception may be Herbert Hoover, one of the great business figures of his age and perhaps the leading manager in political history.

What is significant here isn’t that Hoover presided over the Great Depression — his role in that is still debated — but that Hoover’s business experience and acumen, and the air of management competence that he cultivated and personified, gave him 444 electoral votes in his battle against a breakthrough candidate much like Obama, Gov. Al Smith of New York, the first Catholic to win the presidential nomination of a major American political party.

Other presidential candidates who have run as managers have failed, making little impact in electoral politics. These include Donald Rumsfeld, who as the recent former chief of G.D. Searle and Co., ran for president briefly in 1988, and Lee Iacocca, who held top positions at both Ford Motor Co. and the Chrysler Corp., and also toyed with running for president. Both said they would have emphasized bringing business values to government, which sounds better in the executive suite than on the campaign hustings.

(A business approach was not part of the electioneering appeal of Gov. George W. Bush, who became the first president with an M.B.A. He ran on his record of partisan conciliation in Texas, his concept of “compassionate conservatism” and his own brand of Western-style politics.)

In his 1988 acceptance speech at the Democratic National Convention, Dukakis made a memorable remark:

“This election isn’t about ideology; it’s about competence. It’s not about meaningless labels; it’s about American values — old-fashioned values like accountability and responsibility and respect for the truth.”

Romney could say almost all of that except for the ideology part, for he has drawn an ideological contrast with the president even without original ideas.

It’s still early

It is, however, relatively early in the campaign. Romney’s formal nomination is still weeks away. His acceptance speech has not yet been written. Both the phrases “New Deal” (from FDR) and “New Frontier” (from Kennedy) appeared in their convention acceptance speeches.

When Robert Frost went to visit the White House in 1958, he presented President Dwight D. Eisenhower a volume of his poems, and on the flyleaf he wrote: “The strong are saying nothing until they see.” Perhaps that applies to Romney, and perhaps for the former Massachusetts governor the road not taken lies ahead.