President Obama on Wednesday will formally announce the most aggressive and expansive national gun-control agenda in generations as he presses Congress to mandate background checks for all firearms buyers and prohibit assault weapons and high-capacity ammunition clips.

The announcement will set off a fierce confrontation with Congress over an issue that has riven American society for decades. Obama’s far-reaching firearms agenda has at best tepid support from his party leaders and puts him at loggerheads with Democratic centrists.

Days before his second inauguration, Obama is seeking to drive the gun debate in a way that contrasts with the accommodating approach he often took during his first term. In the weeks ahead, he will attempt to rally popular support to bend the will of lawmakers to vote for what he considers the ideal, not merely the possible.