Case #1: If you are running for Congress against a Republican incumbent. You say: my opponent voted for the Ryan budget that would destroy Medicare.
Case #2: If you are an incumbent Democrat who voted for the grand bargain. You say: my opponent supported the Ryan budget that would destroy Medicare.
Case #3: If you are Barack Obama. You say: my opponent supported the Ryan budget that would have destroyed Medicare.
In case 1, if pressed by reporters, you say: I support deficit reduction, but I oppose Medicare cuts and [insert any and all specific cuts that have been raised by the reporter or which harm your district], and I oppose the Ryan budget that my opponent and other Republicans in Washington support that would destroy Medicare.
In cases 2 and 3, if pressed by reporters, you say: I got our budget under control. As far as Medicare, I supported modest cost-savings, but my opponent supports the Ryan budget, which would destroy Medicare.
Note: I am not suggesting that Democrats should (or, for that matter, shouldn't) agree to Medicare cuts as part of a grand bargain; and, for what it's worth, I agree with Scott Lemieux that the White House is nuts if it believes that a grand bargain will help in any significant way in November 2012. But the idea that a grand bargain including Medicare costs would prevent Democrats from running against Ryan in 2012 is just wrong.