That's not horrible thinking, but I imagine that's what the Dems were thinking when the Republicans had the White House and the Congress and they gained seats the first time around. Of course, that ended up disintegrating after 6 years; events have a way of throwing odd statistical "certainties".
Other 2002, name a mid-term election where the party in the White House hasn't lost seats, And, you seem to forget that the Republicans have lost a considerable of seats during Bush's term in office.
And, Giuliani is guaranteed to drive social conservatives in the south back to the Democratic party and realign the parties pre-1994, something that would take years for the Republicans to recover from.