Controversial gun legislation cleared a key Senate hurdle Thursday, as lawmakers voted 68-31 to start debate on the package which includes expanded background checks and new penalties for gun trafficking.

Senate Democrats, joined by 16 Republicans, were able to overcome an attempted filibuster by GOP senators opposed to the current bill. Those senators could still slow-walk the debate, but the Senate will eventually begin votes on amendments -- one of which is considered crucial to winning support for a final vote.

The White House called Thursday's tally an "important" but "early milestone," as both sides of the issue prepare for a grueling debate -- one that is being waged in Washington and on the airwaves.

The amendment likely to be at the front of the line is one from Sens. Joe Manchin, D-W.Va., and Pat Toomey, R-Pa., which would scale back the call for universal background checks. The plan would expand checks to gun-show and Internet sales, but exempt certain personal transactions.