Each of the three top-tier Democrats are hoping to win tonight's caucuses. But what if the "winner" only out-polls the second-place finisher by, say, one percent of the vote? And what if all three end up within a few percent of each other? For Edwards, anything short of a clear win might be fatal. But both Obama and Clinton could both survive a second-place finish — and maybe even third — as long as the margin is very close. Among Republicans, coming in first is critical for both Romney and Huckabee. But another "winner" will be the third-place finisher, which is why John McCain, so resurgent in New Hampshire, swooped into Iowa for a surprise campaign swing yesterday. If Fred Thompson places worse than third, his campaign may be over. Then there's Rudy Giuliani. With his strategy of concentrating on winning the big states that vote on Jan. 29 and Feb. 5 while largely ignoring Iowa, he could well place last in today's caucuses and still become the Republican nominee. If that happens, Iowa's days of outsize importance in the presidential selection process may be over.