Can Toomey beat Specter in a general election?
Depends. Specter has annoyed a lot of folks, but he has the advantage of name recognition and lack of aggressive competition.
PA isn't as party loyalist as some folks are. Hell, when the Dems internally disagreed too much over electing a speaker for the House, the compromise was to put a Repub at the job (of a Dem controlled House, mind you). It was a short term thing, but barely raised an eyebrow.
Mind you, the rest of the post is coming from someone active in the PA Democratic Party.
As much as it annoys people, we will put our own interests ahead of party lines. Especially if those party lines are coming from the federal level. If folks think Toomey will just toe the GOP party line without regards to his actual voters, then he's dead in the water. Bob Casey Jr is a Dem, mostly toes the Dem party line when it doesn't blatantly matter, but he doesn't tend to stab us in the back either. Much stronger 2A supporter too. Keeps a nice low profile and doesn't screw us over too badly. That's essentially all we care about.
We're not going to do a recall and most folks are just waiting to see what happens at election time. IF the dems as a party start to majorly screw up, they'll be tossed out. The dems got a lot of seats because the Repubs pissed off a lot of folks during the Bush years. The anti-Bush backlash honeymoon is almost over. Not quite, but close.
They will lose seats if they burn their political capital on one more unpopular subject. Bailing out the banks and the auto industry burned a lot of the public goodwill. If they pretty much do nothing politically aggressive until the next election, they'll hold power. Maybe lose few seats, maybe gain a few. No big change. If they pick a sensitive issue and run with it, they'll lose big. A gun ban, amnesty bill, or another huge spending bill and they're dead come next election.
At a state level, we have the lovely opposite problem. Folks are annoyed at our guv, and unless he Does Something to pander to Philly, he's gone come re-election. He knows it, which is why he's sucking up to Philly with the anti-gun rhetoric. Unless he's dumber than a box of rocks, I think he wants to loudly squawk about guns to get philly, but not actually sign anything so the rest of the state really wants to toss him out. Unless the opposition sucks, which is always possible.