FRANCONIA NOTCH, N.H. — This year’s New Hampshire primary was a dud. The presidential candidates roared out of Iowa, spent a mere five days in New Hampshire, then careered down to South Carolina. The vaunted first-in-the-nation primary was reduced to a drive-by.

But in a nation with no second acts — the line belongs to F. Scott Fitzgerald, who spent a memorably boozy Winter Carnival at Dartmouth while working on an execrable screenplay with Budd Schulberg in 1939 — New Hampshire is being granted a second chance. The Granite State is emerging as the most unlikely — and in some ways one of the most indispensable — of variables in both parties’ political calculus for the autumn election.

The reason: a peculiar combination of personalities and politics that is transforming a state that is usually ignored in general election campaigns into a serious battleground.

Here are the elements of this new post-primary prominence: New Hampshire was the only state to move from the Republican column in the so-close 2000 election into the Democratic column in 2004. A former Democratic governor, Jeanne Shaheen, is mounting a very strong challenge in a rematch of the contest she lost in 2002 to Senator Sununu, a Republican. Another onetime officeholder, Jeb Bradley, a former two-term Republican representative, is the most likely challenger to the woman who defeated him in a House race two years ago, Rep. Carol Shea-Porter, a Democrat.

All of this is occurring in a state with two remarkable characteristics: New Hampshire is one of the few small, mostly white states that Senator Obama lost in his bruising primary fight with Senator Clinton. And New Hampshire is arguably one of Senator McCain’s strongest states, and certainly his favorite outside of Arizona.

It was in New Hampshire that Mr. Obama’s post-Iowa momentum came crashing back to Earth in January, in part because of Mrs. Clinton’s comeback history here — this is the state where her husband resuscitated his 1992 campaign with a strong second-place finish after the contretemps involving charges he had an affair with a TV newswoman, Gennifer Flowers — and in part because of Mrs. Clinton’s humanizing, teary-eyed encounter right before the primary in a Portsmouth coffee shop.

But more important, it was here that Mr. McCain found his campaign legs, both in 2000 and in 2008. The first time around he skunked President Bush, beating the Texas governor by 19 points in one of the most stunning performances in a state that prides itself on delivering stunning verdicts. In 1996, Patrick Buchanan defeated Senator Dole here.

Eight years later, Mr. McCain affirmed his position as the Republican to beat when he delivered a rare defeat to a Massachusetts politician seeking to use New Hampshire to catapult himself to political prominence.

In a parade of Bay State politicians who sought New Hampshire’s approbation that included John F. Kennedy (1960), Henry Cabot Lodge (1964), Michael Dukakis (1988), and Paul Tsongas (1992), only Senator Kennedy (1980) and Governor Romney (2008) failed to win here.

By defeating Mr. Romney in his backyard — that is a literal statement, as Mr. Romney owns a vacation home here — Mr. McCain delivered two messages: He was a legitimate presidential candidate; Mr. Romney was not.

The fall election in New Hampshire is not so much a race to the middle, which it is in many states, as a race for Independents, who in this state are not necessarily in the middle.

New Hampshire allows Independents to vote in either state primary, and both Messrs. McCain and Obama already have attracted some of them. But some Independents voted for Mrs. Clinton as well — and the very act of an Independent going for a Democrat other than the eventual nominee offers evidence that Mr. Obama may have a tough time here.

On the other hand, this onetime Republican stronghold two years ago delivered both houses of the state legislature to the Democrats for the first time in a century and a third.

Today, Republicans outnumber Democrats by only 12,444 votes in New Hampshire. And while the Republicans claimed 271,220 registered voters this winter, some 355,498 were undeclared. This is now a classic swing state.

Between 1948 and 1988, the Republicans won New Hampshire in every presidential election except for the 1964 Lyndon Johnson landslide, when no Northern state went for Barry Goldwater. That record was built in the face of two elections in which Massachusetts politicians, Messrs. Kennedy and Dukakis, were the Democratic nominees.

The state went Democratic in the two Bill Clinton races, in 1992 and 1996. But it returned to its Republican roots in 2000 only to switch back to the Democrats four years ago. That was an exceedingly narrow victory, only 9,274 votes, and it required the return of Sullivan and Coos Counties, both choking with old mills and ancient industries, to pull it off. For this fall, there are two uncertainties, and they bear the same description: economic.

Already we know that the summer tourism trade, such an important element of the state’s identity and economy, was hurt by high gasoline prices. Before storekeepers counted their receipts this summer, they watched the traffic jams outside their doors and found them wanting. And it is a reasonable guess that in a state where so many people heat their homes with oil, the price of energy is going to be a factor.

Both suggest advantages for Mr. Obama, but this is a state where not only the Independents take pride in their independence.

It is easy to scoff at the notion that a tiny state like this can wield power out of proportion to its size. But remember: In the 2000 election, Ralph Nader won 22,198 votes here, or nearly 4%.

Had he not run for president and had Vice President Gore won at least two-thirds of those Nader votes, which is exceedingly likely, Mr. Gore would have been president, and the phrase “hanging chad” would never have become part of American lore and the American lexicon.

© 2008 The Pittsburgh Post-Gazette