Can states' rights work for liberals? It has always been a conservative cause. Conservatives use states' rights to resist federal policies that protect civil rights, voting rights and abortion rights. Today, however, federal action is often blocked. So progressive states are passing laws that bypass gridlocked Washington and advance the liberal agenda on their own.

In his famous keynote address at the 2004 Democratic convention, Barack Obama criticized pundits who “like to slice and dice our country into red states and blue states.” His rejoinder: “I say to them tonight, there is not a liberal America and a conservative America — there is the United States of America.”

Obama was wrong. Americans have become more and more politically segregated over the past 50 years. Since the 1960s, politics has come to reflect lifestyle and values, and people often choose to live among others who share their lifestyle and values. And therefore their politics.

The number of competitive states has diminished. In the 1960 presidential election, there were 24 battleground states where the margin of victory was five percentage points or less. In the 2012 election, using the same criterion, there were only seven (Ohio, Florida, Colorado, Iowa, Virginia, North Carolina and Pennsylvania). Red states like Texas and South Carolina don’t have a single statewide elected Democrat. Blue states like California and New York don’t have a single statewide elected Republican.

The policy gap between red America and blue America is growing. Look at Obamacare. Sixteen states, plus the District of Columbia, have set up state-run insurance exchanges, as the Affordable Care Act invites them to do. Fifteen of those 17 states, including D.C., voted for Obama last year. States running their own insurance exchanges are experiencing a fairly smooth transition to the new healthcare law.

Twenty states want nothing to do with Obamacare. They’re letting the federal government run the program. Sixteen of those 20 states voted for Mitt Romney last year. In 14 states, the new law is being implemented by a federal-state partnership. Those states split in last year’s election — eight for Obama, six for Romney.

The Affordable Care Act also invites states to expand their Medicaid coverage for the poor. The federal government will bear 90 percent to 100 percent of the cost. The expanded program would give health insurance to everyone with incomes up to 138 percent of the federal poverty level ($23,550 for a family of four). With Medicaid expansion, about half the nation’s uninsured population would get health insurance coverage.

But the Supreme Court ruled in June that states may opt out of Medicaid expansion. Twenty-five states did. Nineteen of them had voted for Romney in 2012. Meanwhile 21 out of 27 Obama states are expanding Medicaid coverage. If you are poor, or near poor, and live in a red state, the new healthcare law probably won’t help you.

Income inequality has been growing rapidly in the United States. Congressional Democrats have tried and failed repeatedly to raise the federal minimum wage, which has been $7.25 an hour since 2009. Nineteen states and the District of Columbia have a higher minimum wage; 15 of them were Obama states in 2012.

In blue America, same-sex marriage is a reality. Sixteen states plus D.C. allow same-sex marriage. All voted for Obama in 2012. Not a single Romney state allows same-sex marriage.

Look at state laws imposing restrictions on abortions. Almost 90 percent of the Romney states have passed laws banning late-term abortions (many of those laws have been enjoined by the courts). Seventeen states provide public funding for medically necessary abortions. Thirteen of them voted for Obama last year.

The Law Center to Prevent Gun Violence grades states from A to F, based on the strength or weakness of their gun laws. Seventeen states were graded A, B or C on gun control. They are all blue states. Twenty-four states got an F. Twenty of them voted for Romney. Red America enshrines gun rights. Blue America means gun control.

We have always had policy differences among the states. That’s what federalism means. What’s happening here is that the divergence between red America and blue America is growing. Progressive states and conservative states are moving farther and farther apart in their policies, just as they are in their politics.

It’s creating two different societies — one where poor people, women and gay people enjoy rights and benefits and the other where they don’t. Does it really make sense that a gay couple can be legally married in Maryland but are no longer married if they move across the Potomac River to Virginia?

We’ve now had four presidents in a row who promised to bring the country together. They all failed. In a famous speech in 1858, when Abraham Lincoln was running for the Senate, he said, “A house divided against itself cannot stand. . . . I do not expect the Union to be dissolved — I do not expect the house to fall — but I do expect it will cease to be divided.”

The division did end. But it took a civil war to end it. If compromise isn’t happening and violence is unthinkable, there’s only one option left: peaceful coexistence in a hopelessly divided land.

Bill Schneider is professor of public and international affairs at George Mason University and a resident scholar at Third Way.