The dynamics of the gun debate in America has seen a sudden change since the horrific massacre at Sandyhook Elementary. While the power was entirely on the pro-gun debate side for the last two decades, public opinion has changed, and Senators must either adapt or perish. A Washington Post/ABC News poll found that 91% of Americans support universal background checks. It's no surprise that the voters are reacting to the 44 Senators who voted against expanding background checks to include all sales online and at gun shows.
It remains to be seen how much the gun vote will play at the ballot box, but Democrats have identified their point of leverage. There will likely be another vote on background checks before the 2014 midterm elections, and Begich will have a tough choice before him if he has to vote on guns again (the others are up for reelection in 2016 or 2018). If these five, from different regions of the country are all getting punished for their votes, it's likely that more senators are as well, and that background checks may be the biggest issue of the 2014 election.