In Pennsylvania, Senator Arlen Specter, a former Republican who converted to the Democratic Party this year, quickly staked out a position in opposition to the troop escalation, while his opponent, Representative Joe Sestak, a former military officer who has been trying to run to the left of Mr. Specter, came out in favor it.  Other House and Senate candidates have seized on the buildup, siding both for and against it, making it likely that the president’s Afghanistan policy will be a central topic in primary races and perhaps general elections as well.  With national liberal advocacy groups already mobilizing against the troop increase, the president’s policy could conceivably prompt additional primary contests against Democratic incumbents, forcing them into races that consume money before general election showdowns with Republicans. Even if they do not instigate primaries, some advocacy groups can be expected to run advertisements and stage rallies against Democrats backing the escalation.  Despite the possible negative impact, Democrats and some experts do see a potential benefit arising out of the party division over how to proceed in Afghanistan.  For the most vulnerable Democrats — those in more conservative states and districts — a vote on the troop escalation presents an opportunity to side with Republicans on a national security issue. At the same time, it would allow a lawmaker to showcase a split with the liberal forces of the party and perhaps — depending on her ultimate view — with Speaker Nancy Pelosi herself.  “That will help some Democrats in moderate districts, because it cuts into Republican opponents running against them as out-of-touch liberals,” said Martin Frost, a former congressman from Texas who headed the Democratic Congressional Campaign Committee during his tenure. “It is harder for a Republican opponent to go after the Democrat in a moderate district who votes with the president on the war.”  Mr. Frost, who was engaged in voter turnout efforts in the last election, said a stance in favor of the buildup could spur criticism from some Democratic constituents. But he said it was unlikely that those voters would then turn around and support a Republican.  “They might make life difficult for the Democrat, but they are not going to stay home,” he said.  Some top Democrats played down the electoral ramifications of Mr. Obama’s Afghanistan policy, saying the president was simply fulfilling his campaign promise to return the American military focus from Iraq to Afghanistan and its potential as a base of terrorism operations.  According to this view, the real test will come in 2011, when Mr. Obama will have to choose whether to follow through on his commitment to begin removing troops from Afghanistan as he presumably starts up his own re-election campaign.  Democratic strategists say that if nothing else, division over the Afghanistan policy could provide a distraction next year when party leaders had hoped to be free to focus on job creation and deficit reduction — two issues with appeal to independents. And a vote on spending $30 billion or more for the additional troops is not likely to come before next spring, pushing the contentious subject even closer to election season.  While Ms. Pelosi acknowledged that Afghanistan is a difficult internal matter for Democrats, she said she did not anticipate that the troop buildup would be an overriding issue in the midterm elections. She said Democrats would be judged more on how they handle persistent national unemployment and the overall economy.  “Meeting the needs of America’s families and seeing the progress that they make is what is important to us and to the president,” she said. “We’ll measure our success in that way and, hopefully, the American people will too in the next election.”
President Obama’s troop buildup is likely to add to Democratic difficulties in what was already looming as a treacherous midterm election.