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.