Former Gov. Howard Dean has an advertisement on the air characterizing his Democratic presidential rivals as failed politicians and captives of the Washington whirl. Sen. Joseph I. Lieberman is criticizing retired Gen. Wesley K. Clark for being indecisive. Sen. John F. Kerry, a decorated Vietnam veteran, is questioning whether candidates who haven’t been under fire in wartime can understand “the experience of being one of those troops on the frontlines when the policy has gone wrong.”

Looks like the campaign has begun in earnest. And with it, two new debates — one tactical, one strategic — have broken out.

The tactical question: Is it smart for members of a party out of office to attack each other in the course of trying to get their party back into the White House? The strategic question: Is it time for the various contenders to make the inevitable midcourse corrections to reflect the hardening reality on the campaign trail?

The answer to both these questions facing the Democrats comes from the greatest Republican of the age, Ronald Reagan. And they came in the classic Reagan manner — in an aphorism and in a joke. The Democrats might do well to listen carefully to both.

As a two-time gubernatorial candidate and a three-time presidential candidate, Reagan practiced what he liked to call the 11th Commandment: Thou shalt not speak ill of a fellow Republican. Maybe because he was a former Democrat himself (and thus familiar with the fondness Democrats have for attacking their own) and maybe because he was so hurt by GOP criticism (neither he nor George Bush ever shook off the sting from Bush’s remark that the supply-side tax theory was “voodoo economics”), Reagan believed deeply that the opposition was in the opposition party, not in his own.

The 11th Commandment is the aphorism. Now for the joke.

Here’s a paraphrase: Two guys are sitting in the woods when a bear approaches their campsite. One of the men starts to sprint. The other lingers at the campsite while he puts on his running shoes. The sprinter looks back and yells: “Why are you putting on those running shoes? You can’t outrun that bear.” The other man answers: “I don’t have to outrun that bear. I only have to outrun you.”

The Reagan joke is particularly appropriate in New Hampshire, where Dean, a neighbor from Vermont, is streaking ahead of the other contenders, including Kerry, the neighbor from Massachusetts. The latest Zogby International poll gives Dean an advantage of more than 2-to-1 over Kerry and puts him at 40 percent. It is possible that Dean’s lead is even bigger than the 23 percentage points Zogby identifies; Dean has drawn support from untraditional sources, and some of his backers may not yet be registered voters. In a similarly crowded field in 1976, Jimmy Carter needed far less (only 28 percent of the vote) to win the New Hampshire primary.

The significance of the Reagan joke is that the campaign, in New Hampshire at least, may have become a race for second place, not for first — a devastating development for Kerry, who might find himself in the position George S. McGovern occupied in 1972, arguing that a second-place finish against a candidate from a nearby state (Edmund S. Muskie of Maine, who took 46 percent of the vote that winter) is pretty darn good. That is an easier case to make if, like McGovern, the second-place finisher is from South Dakota than it is if the second-place candidate is from Massachusetts, source of so many new residents in southern New Hampshire and so much slop-over television news programming.

Kerry also finds himself in a difficult position in Iowa, where Dean and Rep. Richard A. Gephardt of neighboring Missouri are fighting for a slim advantage with just over 20 percent of the vote each. Kerry is a distant third at 9 percent.

The result nationally may be a campaign much like the Republicans’ in 1996, where it became clear that one of the principal figures would be an ideologue (Patrick J. Buchanan, who ended up winning the New Hampshire primary in a campaign marked by his invitation to his supporters to “mount up and ride to the sound of the guns”) and the contest was over who would be left. Sen. Bob Dole of Kansas was the remainder man — and the eventual nominee.

So now the Democrats have to figure out whether they strengthen their case by criticizing each other or whether they, instead, simply weaken their party. The standard answer is that a difficult primary battle toughens up a nominee for an even more difficult general-election campaign. Presidents Humphrey, McGovern, Mondale and Dukakis don’t agree.

The heart of the matter is that, under attack or not, Howard Dean is no longer a phenomenon but a serious candidate for the Democratic presidential nomination. This is a source of some surprise to the Democrats, who for months regarded him as a curiosity and not a contender, and of some comfort to the Republicans, who for months have believed that he would be easier to defeat than Kerry or Clark. For both the Democrats, who no longer need to outrun the bear, and the Republicans, who need to begin to pay attention to it, this is the time to make important strategic adjustments.

David Shribman is a columnist for the Pittsburgh Post-Gazette.