Democratic Senate campaigns in North Carolina and Louisiana are hoping to attract campaign contributions after the conservative group Americans for Prosperity this week launched a $2 million-plus attack ad blitz against them.

Americans for Prosperity, a super PAC backed by the conservative Koch family, purchased $1.7 million in ads attacking Sen. Kay Hagan, D-N.C., and $500,000 in ads against Sen. Mary Landrieu, D-La. Ads in both states criticize the senators for their support for Obamacare.

The senators, however, are hoping that the attacks and the connection to the Koch brothers will stir their own contributors to give more.

"Hitting our goal was important before," Hagan's campaign said in a fundraising email sent Thursday. "Now, it's essential. Fighting back against a buy like that is non-negotiable — we have to do it. And it won't come cheap."

A fundraising message from Landrieu's campaign echoed that urgency.

"Tea Party Republicans throughout the country energized their base with their [government] shutdown and used that energy to increase their fundraising — and we just learned that an out-of-state attack group funded by the Koch brothers is spending millions on a new ad campaign that targets us," the email read.

The ad buys are significant ones at this early stage of the mid-term campaigns, more than a year out from Election Day, and foretell the magnitude of spending by outside groups that will likely be seen in the most competitive 2014 Senate races.

Landrieu and Hagan are top targets for Republicans looking to unseat Democratic incumbents and take control of the Senate.