So what should we make of John McCain's New Hampshire victory last night? What does it suggest for McCain about the road ahead?

Unquestionably, it left the GOP race wide open, gave a new credibility to McCain's once-moribund candidacy, and put him back on a track that could lead to the nomination. Nonetheless, a close look at the exit polls and the demographics of his victory reveals that a host of hidden dangers lie ahead for him in the upcoming primary and caucus states.

For one thing, McCain's percentages of both the Republican and independent voting blocs were lower than they were in 2000, according to CNN's exit polls. That year he won 38% of the Republican vote and 62% of the independent vote, for a 49% victory overall. This year, it was only 34% of the GOPers and 40% of the indies, for 37% overall.

This is significant for the upcoming races because he'll need GOP base support in upcoming Republican-only primaries in many states — and suggests that his work on immigration reform, among other things, has significantly eroded his support among that demographic. It also suggests that his traction with independent voters wasn't what it was in 2000 — a key constituency for McCain in other states.

And that's not all.

New Hampshire is also a state where reducing the deficit took priority over cutting taxes among Republican primary voters by a 54%-44% margin. McCain won the deficit-hawk vote 46%-26% against Mitt Romney, but lost the tax-cutters by 37%-27%. This serves as a reminder that the supply-side crowd has never truly forgiven McCain for his vote against the 2001 Bush tax cuts.

This suggests more perils in the race ahead, because in states like South Carolina and Florida, it's likely that GOP rank-and-file voters will be more sympathetic to the tax-cutter position than the deficit-hawk one, because of the tendency of Southern and farm-belt conservatives to like both federal subsidies and big tax cuts. That means McCain will have his work cut out for him at winning those voters over in a way he didn't in 2000, before his Bush tax cut vote.

There's still more. If you look at what the exits have to say about the ideological breakdown of yesterday's vote, this also suggests problems ahead. In 2000, he won the conservatives with 37%, but this time only got 30% to Mitt Romney's 38%. And CNN puts him at a dead heat against Romney's 35% of core Republicans. This suggests that even if McCain did eke out a win in independent-rich New Hampshire, if anything he's still slipping among conservatives and core Republicans. That's a major problem for him in states like California and Florida, where independents can't vote and the social conservatives who are gravitating towards Mike Huckabee or Romney will dominate the process.

The real significance of McCain's New Hampshire win may be that it will enable him to win some GOP establishment support, something that seems possible again with Rudy fading and Mitt Romney seriously on the ropes. McCain, of course, will need this establishment support for fundraising purposes and to turn insider chatter to his advantage.

But it remains to be seen whether McCain will be able to attract the grassroots Republican primary constituencies that he really needs to put together an electoral victory and win the nomination. And yesterday's exit polls suggest that he has a long road ahead of him on his way to the St. Paul convention.