Senate contests in the presidential battlegrounds of Wisconsin and Virginia, where Democrats had leads in polls a few weeks ago, are now essentially even and could be especially influenced if Romney performs well in those states. Polls show Democratic incumbents in Ohio and Florida still ahead, but those races have tightened as Romney has gained ground in the states. And the Senate races in Connecticut and Pennsylvania, long thought to be safe wins for Democrats, have become real contests.

The parties and independent groups are now investing heavily in a remarkably long list of states stretching from Maine to Hawaii…

To secure a 51-seat majority, Republicans need to win eight of the nine closest races, including protecting four of their seats where contests are hot. Those include the campaigns in deep-blue Massachusetts, where polls show Democrat Elizabeth Warren now ahead of Republican Sen. Scott Brown, and in Nevada, where Sen. Dean Heller (R) is locked in a tough reelection battle against Rep. Shelley Berkley (D).

But Romney’s rise is giving the GOP new hope. New enthusiasm for the presidential nominee could help in Virginia, Ohio, Florida and Wisconsin.