Food for Thought: Supreme Court justices and Mid-East entanglements aside, the mid-term election of 2010 is arguably more important than the Obama-McCain race this year. Those elections will determine who gets to draw the lines in most states for the next reapportionment, something which would give the Democratic Party long-term hegemony in Congress.
This could be further underlined if the party does well in the congressional elections this year, as seems likely even if McCain should win.* Since the party out of the White House tends to gain seats in mid-term elections, the Democratic Party would not only add to what is becoming a sizable majority in the House, but could even further marginalize the GOP in the Senate, where they would have to defend 19 of the 33 seats.
On the other hand, an Obama victory in November would put the Republicans in a more advantageous situation in 2010. It is not difficult to imagine that the new President's honeymoon would not be much longer than Clinton's was in 1993. A repeat of the 1994 debacle for the party would enable the Republicans to regain control of the state capitals, and with it the power to gerrymander the Democrats out of power in the House.
*Having an unsuccessful candidate at the top of the ticket is not always a death knell for the party. Presidential coattails were nearly non-existent in 1984, 1988, 1992 and 1996. In 2000, the Democratic Party actually gained four seats in the Senate while Bush was "winning" his first term. Going back even further, the Party picked up a pair of Senate seats in 1972, including knocking off four Republican incumbents, with George McGovern as the nominee; the ability of the man at the top to bring in new voters, then and now, seems to trump all other considerations.