Criticism of Mitt Romney for lacking a coherent message is grossly unfair. He has been forthright, consistent and even eloquent in pressing home his campaign’s central theme: Mitt Romney desperately wants to be president.

Everything else seems mushy or negotiable. Romney is passionate about the need, as he sees it, to defeat President Obama — but vague or self-contradictory as to why. The lyrics of “America the Beautiful,” which Romney has recited as part of his standard campaign speech, don’t solve the mystery; Obama, too, is on record as supporting spacious skies and fruited plains.

Beyond personal ambition, what does Romney stand for? Obviously, judging by Rick Santorum’s clean sweep Tuesday, I’m not the only one asking the question. I suspect an honest answer would be something like “situational competence” — Romney boasts of having rescued the 2002 Olympics, served as the Republican governor of one of the nation’s most Democratic states and made profitable choices about where to invest his money. But with the economy improving and the stock market soaring, Romney’s president-as-CEO argument loses whatever relevance it might have had.

To conservative groups, Romney can sound like a true believer who never met a tax or a labor union he could abide — and not at all like a “Massachusetts moderate,” which is what Newt Gingrich claims Romney really is.

But Romney will never be able to match Gingrich’s record, for better or worse, as one of the key figures in the development of the modern conservative movement. And Romney — who once was pro-choice — will never be able to get to the right of Santorum on social issues.

The intended centerpiece of the Romney campaign — his 160-page economic plan — is really just a list of proposed measures with no discernible ideological framework holding them together. “Any American living through this economic crisis will immediately recognize the severity of the break that Mitt Romney proposes from our current course,” the candidate promises on his Web site. But much of what he pledges to do on “Day One” has already been accomplished, or is promised, by Obama.

Romney wants to cut the corporate tax rate; Obama has said he wants to lower rates while also closing loopholes.

Romney wants to forge new trade agreements; Obama signed into law free-trade pacts with South Korea, Colombia and Panama.

Romney wants to weed out burdensome regulations; Obama has such a project underway.

Romney wants to survey and safely exploit U.S. energy reserves; Obama says essentially the same thing.

To be sure, some other initiatives Romney promises on Day One would take us in precisely the wrong direction. He would ask Congress for a gratuitous $20 million budget cut that would fail to make a scratch, let alone a dent, in the deficit. He would propose ending the federal role in job training, thus abdicating presidential responsibility for meeting one of the central challenges facing our economy. He would sanction China for manipulating its currency — and, perhaps, launch a needless trade war. He would seek to discourage the use of union labor on government projects, purely as a sop to the conservative GOP base.

And, of course, Romney wants to repeal the Patient Protection and Affordable Care Act, whose centerpiece, the individual insurance mandate, was pioneered in Massachusetts. By Romney. Who continues to defend the mandate as a good idea — too good, apparently, for the rest of the country.

My point is that even Romney’s sharp disagreements with Obama’s policies don’t add up to a philosophy or a vision. They’re more like what stuck after a bunch of random tough-sounding positions were thrown at the wall.

On foreign affairs, Romney offers a lot of blah blah blah about “restoring the sinews of American power” and the like, but nothing as distinctive as, say, Santorum’s extreme hawkishness on Iran or Ron Paul’s isolationist call to bring the troops home from just about everywhere. It’s hard to find any substantive differences between what Romney would do and what Obama is already doing.

Romney does accuse Obama of “appeasement,” and perhaps the charge would have some credibility if Obama hadn’t ordered the raid that killed Osama bin Laden, or used unmanned missile-firing drones to decimate the international jihadist leadership, or helped eliminate dictator Moammar Gaddafi, or demonstrated in countless other ways that whatever else he might be, no one can call him some kind of flower-power peacenik.

One distinction — and, really, this may be the most original position that Romney takes on anything — is that he has ruled out negotiations with the Taliban and apparently wants to extend the U.S. troop commitment in Afghanistan indefinitely.

Wish him luck with that on the campaign trail. He’ll need it.