With each new poll, it’s becoming clear that the United States is shifting to the left. A majority of Americans now supports same-sex marriage. And legalization of marijuana. And normalization of relations with Cuba.

Gallup reports that, in 2013, the percentage of Americans identifying themselves as liberals reached its highest level since 1992. True, it’s only 23 percent. Conservatives, at 38 percent, still outnumber liberals. But the trend has been slowly and steadily upward for liberals since 1996, when it was 16 percent.

This shift is due entirely to Democrats becoming more liberal — 29 percent of Democrats in 2000, 43 percent in 2013. At the same time, Democrats have won the national popular vote in five out of the six presidential elections since 1992 (all but 2004). Barack Obama won a majority of the popular vote twice — something Bill Clinton couldn’t do.

The New America has come to power. It’s a coalition of 10 Democratic constituencies that united to elect and re-elect Obama: young voters, working women, single mothers, African-Americans, Latinos, Asian-Americans, Jews, gays, educated professionals and the “unchurched” (the nearly one in five Americans who have no religious affiliation). Eight of those 10 constituencies — all but Jews and African-Americans — are growing as a percentage of the electorate.

Democrats now have the advantage in presidential elections. You can’t say Democrats have a lock on the presidency, however. There are too many other factors involved, like the state of the economy and the appeal of the candidates. But Democrats are well positioned to keep the White House.

Republicans are equally well positioned to keep control of at least one house of Congress. The Democrats’ presidential advantage disappears in congressional elections like this year’s midterm.

Why? Democrats like to blame redistricting. Republicans won a sweeping victory in 2010 state elections, and that enabled them to control the redistricting process in many states. In 2012, Democrats slightly outpolled Republicans in the nationwide vote for the House of Representatives — but they ended up with fewer than half the House seats.

Redistricting is certainly part of the Democrats’ problem. But it’s not all of it. Incumbency still has a big impact on House elections, and most incumbents are now Republicans.

Democrats also have a geography problem. They tend to live in crowded cities where congressional districts produce big Democratic majorities. That means a lot of wasted Democratic votes. Democrats also live in isolated college and industrial towns — where their votes are often swamped by Republicans in surrounding suburbs and rural areas.

After researching the issue, two political scientists concluded, “the Democrats’ geography problem is bigger than their gerrymandering problem.”

Democrats do better in Senate elections, but their Senate majority is very much at risk this year. The Democrats’ problem in the Senate is not gerrymandering. It’s the Constitution. Small conservative states are entitled to the same two Senate seats as California and New York.

Republicans are becoming a congressional party. The GOP is entrenched in districts and states dominated by the Old America — older, whiter, more religious. You can see it most clearly on the issue of immigration reform. Republicans who worry about capturing the White House know they have to improve their standing with Latino voters. Without Latino votes, Obama would have lost in 2012. But Latinos want nothing to do with a Republican Party that is culturally insensitive to them.

Yet the Republican-controlled House refuses to consider the comprehensive immigration reform bill passed by the Senate last year. House Speaker John Boehner (R-Ohio) has declared immigration reform dead for 2014. The conservative base is resolutely opposed to any immigration measure that includes legalization or a path to citizenship for illegal immigrants. Republicans who vote for such a policy would find themselves facing a tough primary challenge.

We now have a new model for getting the Republican House to pass policies that are acceptable to the president and Senate. They have to win with solid Democratic support plus enough Republicans to squeeze out a majority. That’s what happened last year with the budget deal and the bill that ended the government shutdown. It happened this year with the farm bill and, last week, with the measure raising the nation’s debt ceiling.

Immigration reform could easily pass the House the same way. All the speaker would need to do is allow a floor vote. But Boehner won’t do that. A Republican House member told The New York Times, “If the speaker had moved forward and forced members to vote [on immigration reform], that would end his speakership.”

Republican congressional priorities trumped Republican presidential priorities.

So we are left with a Democratic presidential advantage and a Republican congressional advantage. That’s a formula for institutionalized gridlock.

The best chance to break that gridlock may not come until after the 2020 election. 2020 is a presidential year. If Democrats do well in state elections that year, that could give them more power over the post-census redistricting. Which could set them up to win control of the House.

But not until 2022.

The new normal in U.S. politics is a liberal presidential agenda blocked by a conservative Congress. And frustration among increasingly progressive voters.

PHOTOS: Vice President Joe Biden (L) and Speaker of the House John Boehner applaud as President Barack Obama finishes his State of the Union speech on Capitol Hill in Washington, January 28, 2014. REUTERS/Larry Downing

Gay marriage supporter Vin Testa waves a rainbow flag in anticipation of U.S. Supreme Court rulings in the cases against California’s gay marriage ban known as Prop 8 and the 1996 federal Defense of Marriage Act (DOMA), outside the court building in Washington, June 24, 2013. REUTERS/Jonathan Ernst