House Majority PAC is going on air with another ad supporting Rep. Nick Rahall (D-W.Va.).
The Citizens United survey shows the GOP delegate taking 44 percent of the primary vote.
After losing a Fla. special election last month, Sink is being wooed again by national Dems.
The retiring Republican is backing former Michigan Senate Majority Leader Mike Bishop (R).
Democratic leadership promised him more campaign funds, CNN's John King said.
Lavern Chatman is running to replace retiring Rep. Jim Moran (D-Va.).
The president will hold a duo of fundraisers next week during a two-day Lone Star State trip.
The big fundraising haul will help him in his race against former Judge Ann Callis (D).
Matt Miller is one of several Democrats vying for the seat.
The group is going after Hispanic voters in the Colorado Republican's district.