The anti-gun trio of Sens. Mike Lee, Rand Paul and Ted Cruz has expanded to 13, providing a big momentum push for a GOP-led filibuster against any new gun legislation on the Senate floor this week, including an expanded system of background checks.

Lee on Monday released the names of the other senators joining his effort, claiming, "The more people learn about the consequences of current gun control proposals, the less they will support the new restrictions."

Significantly, Sen. Marco Rubio joined the Lee-Paul-Cruz plan to demand that 60 votes be required to move any new gun legislation out of the Senate, effectively a filibuster because there aren't 60 votes yet for gun control measures. Gun restrictions face an even higher hurdle in the House.

President Obama and Democrats are launching a PR campaign this week to win wider support for anti-gun legislation, which has been waning.

Lee and other Republicans claim that none of the new anti-gun rules being considered in the Senate would have changed the situation in Newtown, Conn. "The proposals serve primarily to limit the rights of law-abiding citizens, while doing little -- if anything -- to reduce violent crimes. Senators have an obligation both to uphold the Constitution and to promote solutions that effectively address national problems. The current gun control proposals fail both tests."

Lee also announced his "Protect2A" project to encourage Americans to use Twitter hashtag #Protect2A to share their thoughts on the Second Amendment.