McConnell's campaign manager, Jesse Benton, highlights three of the new measures in the push for gun control: what he characterizes as "the Feinstein Gun Ban," Sen. Dianne FeinsteinDianne Emiel FeinsteinYouth climate activists march outside California homes of Pelosi and Feinstein Cosmetic chemicals need a makeover Progressives want to tighten screws beyond Manchin and Sinema MORE's (D-Calif.) legislation to ban certain types of weapons, which Benton says "will criminalize firearms by how they look"; a "thinly-veiled national gun registration scheme hidden under the guise of 'background checks"; and a ban on large ammunition magazines.

"It is almost hard to believe the sheer breadth and brazenness of this attempt to gut our Constitution," Benton writes.

And the email pledges that McConnell will oppose any extended gun-control measures, asking supporters to sign a petition opposing the expanded measures outlined in the email. McConnell's campaign also launched a phone recording last week of the senator pledging to block gun-control measures, which went out to gun owners and hunters across Kentucky, according to USA Today.

When supporters sign that pledge, the site redirects to a page to donate to McConnell's campaign.

McConnell is well-positioned for reelection in 2014, with nearly $7 million cash on hand and no evident challengers emerging. But a poll taken by a Democratic firm in December indicates the senator could be vulnerable, as he was ranked the nation's least popular senator and didn't break 50 percent against any of the possible Democratic challengers polled.