Editor's note: Reihan Salam, a CNN contributor, is a columnist for Reuters; a writer for the National Review's "The Agenda" blog; a policy adviser for e21, a nonpartisan economic research group; and co-author of "Grand New Party: How Conservatives Can Win the Working Class and Save the American Dream."
(CNN) -- Wednesday's presidential debate might very well give Mitt Romney a significant boost, but the former governor still faces a difficult path.
One of the more intriguing aspects of the 2012 election is that Mitt Romney might win a substantial majority among white voters while still losing the presidential election. Regardless of the outcome of this election, the rising minority share of the electorate will force a deep rethinking of Republican strategy.
Back in 2008, John McCain won 55% of the non-Hispanic white vote against 43% for Barack Obama. It is worth noting that Obama increased the Democratic share of the white vote by 2 percentage points relative to Sen. John Kerry, the 2004 Democratic presidential nominee.
At the same time, Obama won 95% of the African-American vote, an increase of 7 percentage points compared with Kerry, and 66% of the Latino vote, an even more impressive increase of 13 percentage points. As Ron Brownstein, editorial director of National Journal and a CNN contributor, has observed, Obama's success among minority voters has put the Republican presidential nominee in a demographic bind.
If we assume that Obama's support among black and Latino voters won't dramatically erode between now and November, Romney will have to outperform McCain by a substantial margin among white voters to win the presidential election. In light of recent Democratic success among college-educated white women and Romney's relatively weak performance among noncollege-educated white voters outside of the South, this will prove challenging.
We see some of these dynamics at play in down-ballot races. In recent weeks, the prospects of a number of Republican candidates for the U.S. Senate have deteriorated.
One of the bigger disappointments for the GOP is the growing gap in the polls between former New Mexico Rep. Heather Wilson, a Rhodes Scholar and U.S. Air Force veteran who is rightly regarded as having been one of the party's most talented female officeholders, and Rep. Martin Heinrich, the Democrat who now represents Wilson's old congressional district.
Republicans have long understood that New Mexico would be a tough race for them. Though a Republican, the charismatic Mexican-American prosecutor Susana Martinez won the state's gubernatorial election in 2010 by a margin of just under 7%, while Barack Obama won New Mexico's electoral votes over John McCain in 2008 by an impressive 15-point margin.
So what might account for the differences in how Martinez and Wilson have been received by New Mexico voters? Part of the story is undoubtedly the fact that the electorate in midterm races tends to be smaller and older than in presidential years, which are more favorable to Democratic candidates.
Another part of the story, however, is that the ethnic composition of New Mexico's electorate has also changed. That is, Latinos will likely represent a somewhat larger share of the electorate in 2012 than in 2010, and it is a safe bet that this share will increase over time.
An Anglo Republican such as Wilson is by no means doomed to fare poorly among Latino voters. George W. Bush, for example, attracted a large share of the Latino vote in New Mexico and in the United States as a whole. Yet Martinez seems to have made deeper inroads into the Latino electorate than Wilson.
Democrats appear to be consolidating recent gains in the largest Latino ethnic groups, including the vitally important Mexican-American constituency. The choice of San Antonio Mayor Julian Castro to give this year's keynote address at the Democratic National Convention was presumably made with this point in mind.
A recent report by Ruy Teixeira and John Halpin of the center-left Center for American Progress -- "The Path to 270 Revisited" -- carefully documents the rising importance of America's nonwhite electorate to the outcome of presidential elections.
Along with Colorado and Nevada, New Mexico is part of a vitally important swing region that had until recent years been Republican-leaning. Teixeira and Halpin argue that the changing demographic composition of these states, and in particular the rising Latino share of the electorate, is a key reason why they have become friendlier terrain for Democratic candidates.
Yet Teixeira and Halpin demonstrate that this dynamic doesn't apply just to the Southwest. In a number of so-called New South states, for example, the rising Latino share of the electorate is occurring alongside an increase in the African-American share of the electorate.
Given the fact that the African-American electorate tends to strongly favor Democratic candidates, there is a distinct possibility that a number of states now considered reliably Republican, such as Georgia, might become competitive in the not-too-distant future.
These larger trends raise two possibilities for future Republican candidates. One is that the GOP should work toward building substantially greater support among white voters. Even as the white share of the electorate decreases, winning a larger slice of a shrinking pie is a viable strategy. The biggest hurdle to this strategy, however, is the cultural polarization of the white electorate.
Among younger white voters, for example, socially liberal views on issues such as same-sex marriage are quite common while older white voters, who have been a bedrock of GOP support, tend to embrace socially conservative views. Reconciling these positions might prove difficult.
Leaving age differences aside, college-educated white voters tend to be less receptive to cultural populism than noncollege-educated white voters.
Although many analysts have suggested that Republicans should embrace liberal positions on various social issues to appeal to college-educated white voters, this might endanger the party's hold on less-educated whites. Some attribute Romney's relatively poor performance among noncollege-educated white voters to a campaign message that caters more to the concerns of tax-sensitive voters than to less affluent voters.
The second possibility, championed by former Florida Gov. Jeb Bush among many others, is that Republicans should redouble their efforts to appeal to Latino voters.
This strategy is often associated with the view that Republicans should embrace comprehensive immigration reform legislation that would create a path to citizenship for undocumented immigrants, a majority of whom are of Latin American origin.
It is not obvious, however, that this strategy would yield significant political dividends, and it would alienate voters who believe that creating a path to citizenship would undermine the credibility of future immigration enforcement efforts.
A deeper look suggests that when you compare Latinos with non-Hispanic white voters of the same income level, the edge that Democrats have among Latinos shrinks. One possibility is that Republicans will improve their vote share among Latinos as Latino households experience greater wage and income growth.
The problem, of course, is that recent years have seen extremely modest wage and household income gains. And so Republicans arguably have a strong political interest in policies that will raise wages and incomes.
There are, of course, other factors. Residential integration, immigrant assimilation and intermarriage could all affect the political landscape in unpredictable ways. But if current trends hold, Republicans have a much greater need to expand their coalition than Democrats.
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The opinions expressed in this commentary are solely those of Reihan Salam.