If this Rasmussen poll is for real, Arlen Specter should give serious consideration to running as an independent, because he's not going to win the Republican Senate primary.
After fending off former conservative Congressman Pat Toomey in a 2004 primary challenge, 51% to 49%, Specter's numbers among Republicans have dropped like a stone. Toomey, formerly the President of the right-wing Club for Growth, now sports a 20-point edge on the ancient incumbent.
Rasmussen. 4/21. Likely voters (GOP). (No trend lines)
Republican Primary
Pat Toomey (R) 51
Arlen Specter (R) 30
Specter's numbers are abysmal for a five-term incumbent: he earns favorable marks from 42% of Republicans, with 55% of Repubs having an unfavorable opinion.
Toomey, meanwhile, has a bustling 66% favorability, with just 19% of Repubs down on him.
If Specter wins the primary, he can (and probably will) beat a Democrat, unless a particularly strong one enters the race. But former Club for Growth captain Toomey will almost certainly lose the general election, as Rick Santorum did in 2006.
Specter will never become a Democrat, so it's basically Lieberman or bust for the Pennsylvania senior Senator. As previously mentioned, he narrowly escaped in 2004, and since then, a lot of Pennsylvania Republicans switched parties to vote in the biggest primary of the era (Clinton-Obama) and haven't come back to the GOP.
Most of those, obviously, were moderate Republicans, and many of them were from Specter's base in the Philadelphia suburbs.
Arlen's got some tough decisions to make. It's either go rogue or go home at this point.