Here’s something that’s missing from most postmortems of the presidential election: The white majority that has helped elect 43 American presidents was marginalized by the coalition Barack Obama amassed on his way to becoming this nation’s 44th chief executive.

A new American majority has emerged from the voting that made Obama this nation’s first black president. Obama was backed by just 43 percent of white voters. His largest percentages of support came from blacks, Hispanics and young whites.

Obama won support from 95 percent of black voters, 66 percent of Hispanics and 66 percent of whites, age 18 to 29. He took most of the white vote in the East but lost it to Republican John McCain in every other section of the nation, according to the Pew Research Center.

No Democratic president has won a majority of white votes since Lyndon Johnson’s 1964 landslide victory over Republican Barry Goldwater, but Obama won a smaller share of that vote than any Democrat elected to the White House since then.

McCain took 55 percent of the white vote, topping Obama by 12 percentage points. When Jimmy Carter won the White House in 1976, he lost the white vote to Gerald Ford by 6 percentage points. In his 1992 victory over George H.W. Bush, Bill Clinton lost the white vote by just 2 percentage points. Four years later, Clinton won re-election while losing the white vote by 3 percentage points to Sen. Bob Dole.

While Obama won the backing of urban whites by 4 percentage points, suburban and rural whites voted for McCain by much larger margins. The roots of Obama’s loss of the white vote — and of the white majority’s marginalization — can be found in the South, where whites overwhelmingly rejected his candidacy.

“White Southern conservatives have been isolated by this election,” said David Bositis, senior research associate at the Joint Center for Political and Economic Studies.

Obama lost the white vote in each of the 11 states of the former Confederacy. He took less than 15 percent of that vote in Alabama, Mississippi and Louisiana, and in Arkansas, Texas, South Carolina, Tennessee and Georgia he got less than 35 percent.

He did a lot better — still without winning a majority of the white vote — in North Carolina, Virginia and Florida, former Confederate states where he won overall.

The significance of this seems to have escaped the notice of analysts viewing this election through the outdated prism of Democratic and Republican Party politics.

Obama’s victory has reshaped this nation’s political landscape.

The Republican Party, comatose and with little chance of resuscitation, comprises a shrinking portion of this nation’s white majority. Its Southern base, recruited into the GOP by Richard Nixon’s cynical embrace of a “Southern strategy” aimed at exploiting the region’s racial fears and bigotry, has become a political albatross.

But Obama’s win is also a warning shot for Democrats.

In the past, the Democratic Party has been much more in sync with organized labor and liberal interest groups than with the millions of new black, Hispanic and young voters who cast ballots for Obama. It would be a mistake for Democrats to assume these new voters will embrace their old ways of doing business.

Obama’s coalition is the political party of the future. It won this election under the Democratic Party’s banner, but there’s no guarantee it will remain there.