So was it "los Latinos que lo ganó por Obama"? (trans: the Latinos who won it for Obama)
Or was it the African-Americans? Or the young voters? Or the women? As always in elections, the numbers tell the story. Barack Obama won 71 per cent of the Latino vote, 93 per cent of the black vote, 60 per cent of the youth vote, and 55 per cent of the women's vote (67 per cent of unmarried women).
Mitt Romney got most of the white votes, and did best among older, white males. The problem for the Republicans, though, is crystal clear: there aren't enough white voters any more to bring them victory -- they now make up just 73 per cent of the total electorate, down from 77 per cent eight years ago, and the numbers are falling further year by year.
Ten per cent of American voters are Hispanic; 13 per cent are black; 20 per cent are under the age of 30. No party can win without their support. As one Republican strategist put it after the results were in: "Demography is destiny."
But here's another statistic that I found particularly telling: 81 per cent of voters who said they were backing the candidate who "cares about people like me" went for Obama. In other words, to win an election, you have to be able to persuade voters that you understand them, their problems and their worries.
They don't have to like you -- Margaret Thatcher, for example, never did well in the "likeability" polls, but she did speak a language that resonated with large numbers of British voters. That's why she won three consecutive elections. And that, the numbers suggest, was a major factor in Barack Obama's re-election victory on Tuesday night.
By the way, while we're on the subject of numbers, I would urge you to take with a large pinch of salt all the stuff that's been written this week about America being more deeply split down the middle than ever before. The numbers tell a different story.
Barack Obama won 50.4 per cent of the popular vote on Tuesday. Compare that to the 50.7 per cent George Bush won in 2004, the same proportion that Ronald Reagan won in 1980, or the pencil-thin 50.08 per cent majority that Jimmy Carter won in 1976.
The truth is that the US has been split down the middle for decades. Which means that you need only a small number of voters to shift allegiance -- or for the country's demographic make-up to change (see above) -- for the White House to change hands.
So is it all over for the Republican party? I doubt it -- after all, just eight years ago, George W Bush won 40 per cent of the Hispanic vote, and with a number of rising Hispanic stars in their ranks, there would appear to be no real reason why Republicans can't start working to rebuild some of that support between now and the next Presidential election in 2016.
Those of you with long memories may remember how during the 1980s and early 90s, after eight years of Reagan, followed by four years of Bush Senior, it became fashionable to say the Democrats would never win an election again. Then along came a man called Bill Clinton, younger, cooler, and saxophone-playing, who turned the Democrats into the New Democrats, and charmed his way to the White House.
Something remarkably similar happened in the UK -- Labour was frequently written off during the Thatcher years, but then along came a man called Tony Blair, younger, cooler, and guitar-playing, who turned Labour into New Labour, and charmed his way to Downing Street.
(A Clinton strategist at the time was reported to have told Labour what the secret of the Clinton makeover had been: "Keynesianism, plus the electric chair.")
History teaches us that parties can re-invent themselves to match changing social realities. So here's a mini-prediction for you: keep an eye on Spanish-speaking Republicans, men like Marco Rubio of Florida, who may very well play an increasingly visible role over the next couple of years.
And here's one other mini-prediction: I doubt the Republicans will ever again choose a multi-millionaire venture capitalist as their Presidential candidate.
I still remember the words of a retired factory worker in deepest rural Ohio, whom I met during my recent US road trip: "As long as rich men run this country, it'll be a rich man's country. And they won't do anything for people like me."