Pittsburgh ? Maybe the Democrats weren’t so smart this winter after all.

It was their idea to “front-load” the presidential primaries this winter and spring. That’s the term political professionals use for a caucus and primary calendar that loads most of the contests onto the front of the schedule. The thinking was that the earlier the Democrats settled on their challenger to President Bush, the earlier they could begin to whittle the president down to size.

The first part of that calculus worked fine. The Democrats, in the political phrase that best captures the year thus far, dated Howard Dean but got engaged to John F. Kerry. And the Massachusetts senator has started to focus the party on defeating the president.

But something else has happened, too. Now that the Republicans know their opponent in the November general election, they are focused, too. They’re focused squarely on Kerry, and it turns out that the ones who are doing the whittling in April are the Republicans.

This past week, Pittsburgh has been the center of the political universe. (Columnists are permitted a certain license. I’m exercising it.) In the space of four days, Kerry, Vice President Cheney and President Bush have cruised through town. It’s made us feel as if we were a test market for a new Procter & Gamble product, which is oddly fitting because this is an age in which political candidates are marketed like soap products. So we’ve seen and heard the pitches the principal figures in the election are offering.

Kerry came to town, lingered in the student precincts that used to be such fertile territory for Democrats, reminded the crowd of his military service during the Vietnam War and attacked Cheney and, by implication, Bush for not serving during the war. A day later, Cheney was here and, in front of a friendly audience at the National Rifle Assn. convention, portrayed Kerry as a candidate of flexible principles.

Score so far: Kerry 1, Cheney 1.

Then, Monday night, President Bush flew into Pittsburgh, and suddenly the score wasn’t even anymore. He flayed Kerry for being “in Washington long enough to take both sides of about every issue.”

Part of the Democrats’ problem is that they are outgunned, 2-to-1, which is as good an argument as any for Kerry to select his running mate in the next 30 days. Assume for a moment that the choice is Rep. Richard A. Gephardt, who is the only plausible contender who satisfies two important criteria: He comes from a state that the Democrats lost in 2000 (Missouri, which Bush carried by more than 78,000 votes), and he actually could swing that state to the Democrats in 2004. If Gephardt flew around the country this week and slammed Bush on jobs or the war, he’d be ignored; for all I know, he’s actually doing that now and getting no attention for it. But if he were the designated vice-presidential candidate, his remarks would be on local television and all over the paper.

So right now, during this awkward interregnum between Iowa’s caucuses and Boston’s convention, Kerry is the political equivalent of a penalty killer.

There are more of them out there than there are of him. But that isn’t the most difficult part of Kerry’s challenge. By clinching the nomination so soon, he’s increasing his exposure to the full power of the Republicans’ assault.

If there were two Democratic candidates in the race, as there often are at this point in the political season, the GOP would be in the position of attacking the Democrats as a party, which is risky business when you consider that the Republicans can’t win the election without some Democratic votes. Because Kerry is alone in the field, the Republicans can focus their attacks on him. They can assail an individual politician, which alienates no one, instead of indicting an entire party, which alienates some of the voters they need in November.

The result is that John F. Kerry is the plumpest pinata in American politics today. He’s being battered by the Republicans, who are making especially damaging inroads with the argument that Kerry, who sometimes sees all three sides to an issue, is a flip-flop artist. One of the GOP’s favorite attack tactics: Quoting Kerry’s remark, in reference to reconstruction efforts in Iraq and Afghanistan, that “I voted for the $87 billion before I voted against it.”

There’s a rational explanation for that comment — if, that is, you believe that the way the Senate, a product of 18th-century rationalism, works is rational — but in the heat of a political campaign there’s neither time nor patience for that. It’s a horrible quote, and Cheney delighted in repeating the line here in Pittsburgh Saturday night.

The Republicans now have seven months to make their argument that there is a long way from the Waffle House to the White House. Indeed, Kerry is far more exposed in late April than Gov. Bill Clinton was in late June a dozen years ago. It wasn’t until July 1992, in fact, that the Republicans settled on their line of attack (“a failed governor from a small state”) against Clinton.

Ordinarily presidential candidates use their nominating conventions as a time to introduce themselves to a nationwide audience; until then, the audience for their entreaties is usually party activists, all of whom end up voting for their party’s nominee anyway. Candidates usually start with a clean slate at the convention and work from there. The early resolution of Campaign 2004 changes the dynamic for Kerry, however. This fallow period means that Kerry is not starting with a clean slate. Instead, his job at his convention will be to wipe the slate clean.

David Shribman is a columnist for Universal Press Syndicate.