(CNN) Alaska's lieutenant governor resigned abruptly Tuesday over what he said were "inappropriate comments" -- which he and other officials have done little to further explain -- providing an unexpected ripple in his boss's re-election campaign just three weeks before voters go to the polls.

Byron Mallott, in a letter to Gov. Bill Walker, said it is "a resignation compelled by inappropriate comments I made that placed a person whom I respect and revere in a position of vulnerability."

"I take full responsibility for this action and apologize to, and seek healing for, the person I hurt," the letter reads.

Mallott, a Democrat, was Walker's running mate when they were elected in 2014 , and the two had been running again on a joint ticket for a second term. Walker is an independent who formerly served in public office as a Republican.

Department of Health and Social Services Commissioner Valerie Nurr'araaluk Davidson was sworn in Tuesday as Mallott's successor. She has represented Native American tribes at the state level under administrations of both major parties, her official biography states.

Read More