Senate Majority Leader Harry Reid (D-Nev.) continued his airwave offensive Friday with the launch of his fourth television ad of the 2010 campaign, another sign that despite his nonchalant attitude, the four-term Senator is aware that his re-election chances are in peril. The one-minute spot is the most direct yet in making what is Reid’s central appeal: that his political clout is too valuable for the state to replace him. “He’s the most powerful Senator Nevada has ever had,— a narrator in the ad begins. “And Harry Reid’s working harder than ever to get Nevada’s economy back on track.— It goes on to list federal funds, tax credits and other pork projects that Reid has delivered to the state.“As the leader of the Senate, my responsibility is to make sure that no one takes advantage of Nevada,— Reid says.Reid’s aggressive advertising pace is enabled by a hefty war chest that the Senator has compiled over the past year. He reported more than $8.7 million in cash on hand at the end of September and has pledged to raise $25 million total for his campaign. Republicans acknowledge that they are likely to be outspent in the race but predict that Reid’s advertising will reach a saturation point beyond which more buys are not going to make much of a difference.A large field of Republicans have emerged to take on Reid, and two of them led the Democrat in recent polls. The primary is June 8.