Vice President Joe Biden, speaking Tuesday at an event in Baltimore, said he was unsure whether there is enough support in the Senate for what would be the biggest change to federal gun laws in decades.
"We may not get it this week, but we will prevail," Biden said of the bill, which senators will vote on Wednesday. Sixty votes are needed to pass the measure.
Police closed city streets and increased security at nearby Penn Station in anticipation of Biden's arrival at an event to preview the University of Baltimore's new law center.
Biden said he considers Baltimore "the best city in America," cracked jokes, then turned solemn as he spoke about the bombings at the Boston Marathon on Monday and the shootings in December in Newtown, Conn., in which 26 people and the shooter died.
The vice president recounted painful conversations with the parents of children killed at Sandy Hook Elementary School, and praised Maryland for passing gun-control legislation, saying he hoped that Congress could follow the state's lead.
Biden expressed condolences to those who lost loved ones in the explosions in Boston.
Biden said the federal government does not yet have "all the data" on the bombings, but that it is using "every resource" to find out who is responsible.
"We will respond to those cowardly acts," he said. "We will find the perpetrators and bring them to justice."
Biden referred to reports of runners who crossed the finish line after the blasts, only to continue running to give blood at hospitals, and the acts of first responders, saying they represented the "extraordinary character of the people of America."
"That's the American character, that's stamped in our DNA," he said.
The university's new $114 million building, like the current law center, is named for the parents of Orioles principal owner Peter G. Angelos, an alumnus of the law school and donor of $15 million of the $22 million in private funding for the building. The rest of funding for the law center came from the state.
Biden spoke of the future attorneys the law school will graduate, and said they will work in an environment where public opinion on social issues such as same-sex marriage is rapidly shifting.
"Our laws evolve; they have to evolve to reflect the will of the American people," he said.