Citizens go to the cast their ballots at the South Shore Park building on election day November 4, 2014 in Milwaukee, Wisconsin. Republican Gov. Scott Walker is running in a tight race against Democratic opponent Mary Burke.National Journal

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The one-sentence explanation of contemporary American politics is that Republicans cannot win enough minority voters to consistently control the White House, and Democrats cannot win enough whites to consistently control the House of Representatives.

(Darren Hauck/Getty Images)Over the past two decades, this dynamic has produced a precarious balance. By 2016, Democrats will have held the White House for 16 of the 24 years since 1992. (Democrats actually won the popular vote in five of the six presidential elections over that period, but lost the Electoral College to George W. Bush in 2000.) Republicans, though, will have controlled the House for 18 of those 24 years. Each party will have held the Senate for half of that period. In this unsettled environment, neither side has amassed a durable edge. By 2016, voters will have provided one or the other party unified control of the White House and both congressional chambers for just eight of the past 24 years, and never for more than four years consecutively.

This complex landscape of fractured authority and offsetting strength has confounded political analysts who wish to confer a decisive advantage on either side. The latest example is my perceptive new National Journal colleague John B. Judis, who coauthored a 2002 book called The Emerging Democratic Majority. In a recent National Journal story, he forecast instead an "emerging Republican advantage."

Judis's article underscores important points about the resistance to activist government spreading across the white working class and middle class. But his conclusion, which conservative analysts have seized upon, oversimplifies the split-level electoral dynamic that is splintering authority between the parties.

That fragmentation of power is rooted in the racial trends noted aboveā€”and also in the overlapping generational and geographical realignments accompanying them. Since 1992, Democrats have built a powerful presidential coalition centered on three groups: young people (especially after millennials started voting in 2000), socially liberal whites (particularly both single and college-educated women), and racial minorities.

I call this alignment the "coalition of the ascendant," because its key components are growing in the electorate. Since 1992, minorities have more than doubled their vote share to 28 percent, and are on track to continue gaining roughly 2 percentage points every four years. Millennials represented less than one-fourth of eligible voters in 2012, but will reach 36 percent in 2020. And with more women than men obtaining degrees, college-educated white women could cast one in five ballots next year, nearly double their share in 1984.

Democratic presidential candidates have consistently performed well with these groups. In 2012, Obama won four-fifths of minorities, and although he slipped relative to 2008 with millennials and college-educated white women, he still carried three-fifths of the former and just under half of the latter. Those showings allowed Obama to overcome Mitt Romney winning more than three-fifths of both older and blue-collar whites. (Critically, though, Obama did better with those two groups in precisely the states where he most needed them: Rust Belt battlegrounds, including Ohio and Wisconsin.)

This demographic alignment doesn't guarantee Democrats permanent White House control; campaigns and conditions count. But if they remain strong with these growing groups, Democrats will retain a presidential edge in most years. In 2012, Obama won comfortably while carrying only 39 percent of whites, the lowest ever for a winner. If the minority vote share follows its projected growth trajectory, and Democrats win the roughly four-fifths of nonwhite voters they have attracted in all but one presidential election since 1976, the 2016 Democratic nominee could assemble a winning national majority with support from just 37 percent of whites.

Exit polls found that Republicans won 60 percent of whites in both their 2010 and 2014 House landslides. If the party's 2016 presidential nominee replicates that performance, he or she would almost certainly lose, absent major advances among minorities. If the GOP doesn't improve among minorities in 2016, its nominee could win only by approaching Ronald Reagan's white showing (64 percent) in his historic 1984 reelection. Realistically, the GOP needs more nonwhite support to regain the White House.

The converse is that Democrats aren't attracting nearly enough whites to win the House. Because minority voters are heavily concentrated in urban areas, whites exceed their national population share in 263 House districts; the GOP holds 199 of them, an insurmountable advantage. Lower minority (and youth) turnout in midterm elections compounds the Democrats' problem. Until they recapture more white voters, they won't retake the House.

At other levels, power is diffused, too. Republicans have opened a commanding lead in state governments, but Democrats control most cities. The U.S. Senate will likely remain closely divided as both parties increasingly dominate seats from the states they usually carry in presidential contests.

Across all these dimensions, each party today is operating with an electoral coalition defined as much by its limits as its strengths. So long as that's true, American politics is more likely to produce a polarized stalemate than a comprehensive advantage for either side.

This article is from the archive of our partner National Journal.

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