Advocacy groups that have pressured congressional Republicans to demand that a new budget measure defunds Obamacare are now turning their sights to Democrats, seeking to pin the blame on them for the government shutdown.

Heritage Action for America announced Thursday that is launching a  $400,000 online ad campaign against four Senate Democrats who face tough reelection fights in 2014: Mark Begich of Alaska, Mark Pryor of Arkansas, Mary Landrieu of Louisiana and Kay Hagan of North Carolina.