Small changes can have dramatic consequences. The electorate shifted about 4 points toward the Democrats in between the 2004 and 2008 elections--from 48.3 percent of the popular vote four years ago to 52.5 percent today. But those 4 points gave Obama the largest share of the vote since 1988, the best showing by a Democrat since 1964, the first black president, the first non-southern Democratic president since John F. Kennedy, and likely larger Democratic majorities in Congress than when President Clinton took office in 1993. In a closely divided America, a swing of four votes in a hundred can mean a decisive victory.

Obama's achievement can be explained with a few numbers. The first is 27 percent--President Bush's approval rating in the national exit poll. Pretty dismal. The poll found that voters were split on whether John McCain would continue Bush's policies. But those who thought McCain would be another Bush broke overwhelmingly for Obama, 91 percent to 8. That's a huge, damning margin.

The second number is 93 percent. That's the percentage of voters who gave the economy a negative rating in the exit poll. They supported Obama. And they were right to give the economy a negative rating. The financial crisis is spilling over into the real economy of goods and services. Unemployment is rising and consumption is falling. The week before the election, the Commerce Department announced that consumer spending had dropped 3.1 percent. Consumer spending hadn't fallen since 1991, and this year's decline was the largest since 1980. The day before the election, the auto companies announced that they had had their worst month in a quarter-century. When economic conditions are as bad as this, of course the party out of power is favored to win an election.

Considering those numbers, the 2008 electoral map isn't all that surprising. Bush, the economy, and Obama's personal and political appeal have pushed the nation toward the blue end of the political spectrum. But, for the most part, the shift is gradual and on the margins. Obama will be president because he took states that Bush won in tight races four years ago. Bush won Ohio by 2 points in 2004. This year Obama won it by 4. Bush won Florida by 5 points in 2004. This year Obama won it by 2.5 points.

Obama's victories in the West were impressive. Bush won Colorado by 5 points in 2004. Obama won it by 7. Bush won New Mexico by 1 point in 2004. Obama won it by a substantial margin--about 15 points. Bush won Nevada by 2 points in 2004. Obama won it by about 13 points.

Virginia has been trending blue since 2001, when Mark Warner was elected governor. In 2004, John Kerry won the Washington suburbs of Arlington, Alexandria, and Fairfax, but still lost the state to Bush, 45 to 54 percent. The next year, another Democrat, Tim Kaine, succeeded Warner. And the year after that, voters replaced incumbent Republican senator George Allen with Democrat Jim Webb in a contest decided by just a few thousand votes. In 2008 Virginia went totally blue. It handed the Democrats as many as three more House seats, replaced retiring Republican senator John Warner with Mark Warner (no relation) by a vote of two-to-one, and swung for Obama by a margin of 5.5 points. Virginia's electoral votes went for a Democrat for the first time since 1964.

The two major surprises on our new map are North Carolina and Indiana. Bush won North Carolina by 12 points in 2004. This year Obama erased that margin and won by a couple tenths of a point. It's the first time since 1976 that North Carolina has voted for a Democratic president. In Indiana the swing toward Obama was even more pronounced. Bush won there by a huge margin of 22 points in 2004. Obama made up all of that ground, eking out a victory of about a point. No Democrat had won Indiana since 1964.