|Sen. Jeanne Shaheen (D-NH)|
Republican Brown has trailed in virtually every poll. But in recent weeks, he's closed the gap to within a couple points of Democrat Shaheen. Shaheen is popular in New Hampshire and has been near the magic 50% in earlier polls. She's dipped a few points and Brown has risen a few to make for a closer race. If the Republicans win New Hampshire, which has long has been categorized as leaning to the Democrats, the Democrats will almost certainly lose in the states where Republicans currently are polling slgithly ahead.
The challenge for Shaheen and Brown is the polls in the Granite State show very few undecided voters, about 5%. So there is not a pool of unattached voters for the candidates to appeal to. They have to persuade voters who are committed to their opponent to switch.
The undecided voters almost always break for the challenger. usually by 2-1 margins, so let's say Brown gets 3% of that 5%. If the poling is accurate, Shaheen would still edge out Brown, albeit barely. So if on Election Night Shaheen loses, it will almost certainly be because Democrats stayed home rather than going to the polls. That would probably be a sign that a wave is coming that would result in not 51 Republican seats but as many as 53.