Last year’s mass shootings have brought renewed focus on gun violence. Though how to stem it remains a politically contentious issue on Capitol Hill, advocates say momentum for reform has reached levels not seen in nearly 20 years. The Senate Judiciary Committee will examine four separate proposals to curb gun violence at a markup Thursday. And House Speaker John Boehner has said that his chamber will consider any legislation that passes the Senate. The change in tone reflects a growing push by activist groups whose support has increased and war chests have swelled following the Sandy Hook Elementary School shooting in December.