Americans for Prosperity, the conservative group backed by the Koch brothers, unveiled a TV ad blitz Thursday attacking vulnerable Senate Democrats over the implementation of Obamacare.

The group launched a $2.5 million ad buy targeting Sens. Kay Hagan (N.C.), Mary Landrieu (La.) and Jeanne Shaheen (N.H.), all Democrats facing tough reelection battles in 2014. The three ads follow a similar theme, zeroing in on some of the struggles the health care law has faced in the early stages of its rollout -- namely President Barack Obama's pledge that individuals could keep their current plans under Obamacare, which later turned out to be untrue.

"It's the lie of the year," the narrator says in the ad targeting Shaheen. Each spot also notes that the senators in question reiterated Obama's "If you like your plan, you can keep it" promise. The woman appearing in the Hagan-directed ad is Sheila Salter, a small business owner in North Carolina who recently said she was so stressed out by Obamacare that it was causing her to drink. The ads will run for three weeks in major media markets across North Carolina, Louisiana and New Hampshire.

Americans for Prosperity released a similar set of ads against two House Democrats last week. The broader campaign is consistent with the overarching Republican strategy to once again focus on Obamacare in the 2014 midterm elections. Conservatives have already seized upon some of the law's initial failures, even though more than 2 million Americans successfully enrolled in the health care exchanges for benefits that went into effect Wednesday.

While Hagan and Landrieu are considered more vulnerable running for reelection in conservative states, Republicans are hopeful that a potential challenge to Shaheen from former Sen. Scott Brown (R-Mass.) would make the New Hampshire Senate race more competitive. Brown said recently he has "nothing to announce" with respect to his political career but confirmed his move to New Hampshire last month, citing personal reasons.

UPDATE: 2:40 p.m. -- Justin Barasky, a spokesman for the Democratic Senatorial Campaign Committee, responded to the ad buy with the following statement:

The Koch brothers spent millions of dollars in 2013 on false TV ads to elect reckless and irresponsible Tea Party Republicans to the U.S. Senate and it looks like they're going to spend even more in 2014. Corporate special interest groups that backed the government shutdown want to elect even more Tea Party Republicans who will privatize Social Security and Medicare and push our country to the brink of an economic default. Our Democratic Senators will continue to fight the Tea Party agenda and work on behalf of their states and constituents.

Watch the Kay Hagan ad here:

Watch the Mary Landrieu ad here: