Personally, I think any big changes made by the opposing party are unlikely in the extreme, but who knows? Maybe they will succeed against all of the odds.
First step: Win back congressional seats in November. Second step, get the Whitehouse back in '12.
Now, who are they going to run in '12? Who is capable of winning the WhiteHouse, particularly if the economic recovery continues until then? There is the first big hurdle to jump.
Of course, after that one, there will be others.