They HAVE to support him... Think about it, if they don't, you'll see the DNC running ads saying that the RNC/GOP didn't support him, after x years of supporting their party. You also risk him switching the Dem side, or withholding votes on major issues...
If Toomey wins, you'll see the GOP/RNC support him 100%.
I heard that Specter was encouraging Democrat constituents to vote for him in the primary. I don't think it's far-fetched imagination that the DNC would run ads advocating exactly the same thing. "Specter, a man we can ALL support!"
I'm not in PA, so don't know what the tenor of the primary campaign is. I do hope Toomey wins, and I do hope the GOP and RNC support him 100%.