White House Press Secretary Robert Gibbs on Wednesday acknowledged that President Barack Obama’s popularity has slipped since he took office a year ago but was optimistic that his supporters will rally behind him and the Democratic Party come November.The lagging excitement among Obama’s core backers could have serious consequences for Democrats, who need a large turnout in the midterm elections to stem losses in the House and the Senate. Liberals have been concerned about the president’s decision to send 30,000 more troops to Afghanistan and to jettison a public insurance option form the health care reform bill, among other issues. But Gibbs predicted that voters will come around. “There’s a lot at stake,— Gibbs said.Gibbs said the president still has no plans to travel to Massachusetts to campaign for Attorney General Martha Coakley (D), who is running in Tuesday’s special election to succeed the late Sen. Edward Kennedy (D-Mass.). Sen. Paul Kirk (D) is filling the seat temporarily. Gibbs spoke as Obama continued to meet at the White House with House and Senate Democratic leaders on health care reform. Gibbs refused to discuss the state of the talks.Meanwhile, Obama cancelled a speech he was scheduled to deliver in Lanham, Md., on “clean jobs— in order to focus on the devastating earthquake that struck Haiti on Tuesday.