Freshman Democratic Sen. Joe Donnelly is opposing a ban on assault weapons sought by President Barack Obama.
A Donnelly spokesman told The Associated Press Wednesday that the Indiana lawmaker will vote against the ban but has not decided whether he would support universal background checks.
Donnelly represents a key bloc of moderate to conservative Democrats the president must win over. The announcement also marks a key early stance from Donnelly just a few months after winning a state that went heavily for Republican presidential candidate Mitt Romney in last year's election.
Donnelly called himself "a strong supporter of the Second Amendment" in a statement issued shortly before the Senate Judiciary Committee opened a hearing featuring testimony from National Rifle Association CEO Wayne LaPierre and former Rep. Gabrielle Giffords.