GOLDEN, Colo. (AP) - As he deals with the anti-American unrest in the Middle East, and the killing of four U.S. diplomatic personnel in Libya, President Barack Obama is continuing his campaign for re-election -- telling a crowd in Colorado that "no act of terror will go unpunished."

He said he's told his administration to "do whatever is necessary" to protect Americans serving abroad.

Obama told the rally, "We are going to bring those who killed our fellow Americans to justice." He said, "No act of violence shakes the resolve of the United States of America."

Mitt Romney today mentioned the crisis only briefly, at the top of his speech in Virginia. He spoke broadly about the need to strengthen American leadership overseas, and he warned that Obama is weakening the U.S. military.

A heckler accused him of "politicizing" Libya, but the heckler was drowned out and then escorted out.

Romney, who faced criticism for his quick attack on Obama as the events in Libya unfolded, has since tried to refocus the campaign on the economy. He had initially suggested that Obama was weak and didn't react quickly enough to condemn the attacks on U.S. embassies. Obama responded by suggesting that Romney is reckless and untested as a world leader.