The Senate is set to take up legislation that would expand gun buyer background checks on the heels of an endorsement from an important gun rights group, and steady pressure from Sandy Hook families.

In an interview with NPR's Robert Siegel, Montana Sen. Max Baucus says he broke with Democrats on gun legislation because he represents the wishes of Montanans and agrees with them.

A pro-gun control superPAC started by former Rep. Gabrielle Giffords and her husband, onetime astronaut Mark Kelly, launched radio ads against Republican Sens. Mitch McConnell and Kelly Ayotte for voting against bipartisan background check legislation.

The opportunistic political sentiment of never letting a crisis go to waste has been reframed since the Boston bombings by those seizing on the attack as certain evidence of their positions. But a national security expert warns against the inclination. "It's difficult to make law by anecdote," he says..