Incumbent GOP Sen. Arlen Specter (search) is fighting for his political life — from within his own party.

Though he has the support of President Bush and his Republican colleagues in the Senate, polls show conservative Rep. Pat Toomey (search) moving within striking distance just hours before Pennsylvania voters were going to the polls on Tuesday.

Specter spent his last day before the election holding press conferences in which he emphasized his seniority in the Senate after 24 years.

But Toomey has been hammering the four-term senator around the state with television ads that are no-holds barred. Toomey is supported by the Club for Growth (search), an advocacy group fighting to lower taxes that has spent $2 million on defeating Specter.

Toomey said he has the energy and momentum to win, but observers say the 10 percent of undecided voters in the state will determine whether Toomey can close a six-point gap he had from Specter in the day before the election.

Bush has a vested interest in a Specter victory Tuesday. If Toomey wins the GOP primary, Democrats will be even more energized to go to the polls in November in a critical swing state that Bush wants to win this year, and in which he was leading by just four points over John Kerry in the latest head-to-head poll.

Click here to watch a report by Fox News' Brian Wilson.