With polls consistently showing President Obama facing even greater resistance from white voters than he did in 2008, he will likely need to maximize his advantage among minorities to win a second term in November.

In that effort, an analysis of recent Census Bureau data offers optimism for the White House. The data, analyzed by Brookings Institution demographer William Frey, show that minorities are continuing to rise as a share of the eligible voter population — and they are making especially pronounced gains in some key swing states for 2012.

Obama's team faces challenges in registering and turning out those voters in a climate that features the combined headwinds of hard economic times and tough new voter-security laws signed by several Republican governors that Democrats see as unabashed efforts to suppress participation.

Some experts are especially worried about Hispanic turnout after the number of Latinos registered to vote fell unexpectedly between 2008 and 2010, probably because of widespread economic dislocation. Registration drives will increase those numbers  in 2012, but starting from a lower base may mean a lower peak than once expected.

Yet, notwithstanding these potential barriers, the long-term trend is that the minority share of the electorate has grown in step with its rising share of the population eligible to vote. "This has been the logic of the past 20 to 25 years of American political history," says Ruy Teixeira, a Democratic voting analyst.

"The minority share of eligible voters should be even higher in November." — Demographer William Frey

In the data analyzed by Frey, the Census Bureau reported that as of January, whites constituted 71.3 percent of the eligible-voter population — that is, U.S. citizens who are at least 18 years old. That percentage has been tumbling since 2000, when whites were 77.7 percent of all eligible voters. It dropped to 75.2 percent in 2004 and 73.4 percent in 2008 — a descent of about 2 percentage points every four years.

Frey says that by November, the white share of the electorate will likely fall a bit further, because about 50,000 Hispanics, the vast majority of them native-born American citizens, turn 18 each month. "The minority share of eligible voters should be even higher in November, especially in states with large Hispanic gains in the last decade like Nevada and Arizona," Frey says.

While African-Americans have remained essentially constant as a share of eligible voters since 2008, Hispanics have increased from 9.5 percent to 10.7 percent, and the broad category of others (that includes Asians and those of mixed race) has edged up from 5.3 percent to 6.1 percent. Hispanics now make up at least 10 percent of the eligible-voter population in nine states; last time, Obama won all of them except Texas and Arizona, and his campaign is targeting the latter this year.

Hispanics and Asians (and, to a lesser extent, African-Americans) turn out at lower rates than whites, so minorities generally account for a smaller share of the vote than their actual eligible-voter population. But the two numbers move together closely.

From 2000 to 2008, minorities increased their share of eligible voters by 4.3 percentage points — and raised their share of the electorate from 21 percent to 26 percent, according to the exit polls. If that correlation holds, the minority share of the vote would rise to about 28 percent this year (which the Obama campaign projects), although a white turnout surge or other factors, such as disappointing Hispanic registration decline and the new voter laws, could stunt that growth.

As the table shows, these gains are unevenly distributed. Many of the states experiencing the biggest minority increases, such as California and Texas, are securely locked in one party's camp. And the white share of the eligible-voter population actually increased slightly in the toss-up states of Ohio and New Hampshire, which could benefit Mitt Romney.

But in other competitive states — including, Arizona, Nevada, North Carolina, Virginia, and even Michigan and Pennsylvania — a growing minority presence could provide a decisive thumb on the scale for a president who is struggling to match even the modest 43 percent of the vote he won among whites in 2008.