(CNN) – John McCain has effectively captured the Republican nomination, but he’s still struggling to win over a key constituency of one: Focus on the Family founder James Dobson, who once said he would not vote for the Arizona senator “under any circumstances.”

Some disappointed conservatives had threatened to stay home on Election Day – but Dobson’s interview Monday may send a message to millions of evangelicals that they should reconsider that decision and head to the polls.

In an interview last night, the evangelical leader told FOX host Sean Hannity that while he has issues with all the candidates left in the race, particularly the Democrats, he would definitely be casting his ballot this fall.

"Let me just say that I will certainly vote,” said Dobson. “I think we have a God-given responsibility to vote, and there are all of the candidates and the issues down the ballot that we have an obligation to weigh in on and let our voices be heard."

But he stopped short of embracing McCain’s presidential bid, and expressed skepticism about his orthodoxy on key conservative stands, asking Hannity skeptically if the senator had given a commitment on stem cell research.

Earlier in the race, Dobson backed McCain’s Republican rival, former Arkansas Gov. Mike Huckabee.