This is generally why Members of Congress do not do well in national elections. Both Al Gore and John Kerry were savaged by their prior records in Congress.
President Obama, of course, was the smartest of them all. His move to the national Senate in 2005 was effectively run in concert with his Presidential run of 2008, and he carefully built a voting record which could not be so easily assailed (he also quickly took in all the Senate rules, which has allowed him and Harry Reid to tie the GOP into knots over the past 18 months).
Ryan's record won't be nearly as pretty. We'll see that he voted against every decent thing that ever came his way in 14 years. We'll see how he tried to shovel Social Security money into the failing housing bubble, how he tried to kill off the poor and old people, and so on.
Add to that a Jesse Helms-like record of incivility so deep that he dared not even introduce a bill in a decade, and it's going to be a turkey shoot. One which he well deserves.