IF Obama wins, there's at least a 65% chance he could get two terms, depending on how stupid people are, and what kind of candidate the Republicans offer. Let's also add here that IF Obama wins, much of the Republican party will be stupid enough to blame Sarah Palin and the more conservative part of the base. That stupidity would almost surely bring a second defeat.
IF Obama wins, it is likely that the turnover in Congress will continue, and the Democrats will gain seats. There will be at the very least constant attempts to legislate new and far reaching firearms restrictions on a very regular basis.
IF Obama wins, and especially if he gets his second term, it is likely he will nominate 2-3 Supreme Court Justices. There is no doubt as to how liberal they will be, how likely they will be to legislate from the bench, and how far they will go to subscribe to the theory that the Constitution is a "living document".
IF Obama wins, you can expect an EXTREMELY liberal and anti-gun Attorney General. Along with this AG, you'll have the same thing throughout the justice department AND in the BATFE. At that point, you don't even NEED new laws, all you need is a little judicial re-interpretation of the current laws, along with rabidly overzealous enforcement policies based on those "new re-interpretations." Ask some of the long term Federal Firearm License holders what life was like under the Klintons and Janet Reno.
It could take 2-4 DECADES to undo the damage, IF it could EVER be undone, outside of a major revolution of some sort.