For decades, and especially during the past seven years, political media have complained about what they say is a lurch toward right-wing extremism by the Republican Party. The rise of the Tea Party, congressional GOP resistance to President Obama's agenda, opposition to gay marriage, the lack of abortion supporters in the party— all of it has been depicted as evidence of extremism and being out of touch with the public.

This superficial and self-serving analysis ignored the existence of the reciprocal phenomenon — the Democratic Party's lurch to the left.

According to a recent American Enterprise Institute report, the ideological make-up of the Republican Party hasn't changed much over the last 15 years. Looking at Gallup data, the researchers found that the share of Republicans who identify as "conservative" increased from 62 percent in 2000 to 68 percent in 2015.

But the percentage of Democrats who self-identify as liberal has risen in that time from 29 percent to 45 percent. The number of white Democrats who identify as liberal has nearly doubled, from 28 percent to 50 percent. The report also found that barely a third (37 percent) of Democrats describe Hillary Clinton as a liberal. About half call her a moderate.

Michael Barone, the Washington Examiner's senior political analyst and an AEI resident scholar who contributed to the report, analyzed exit poll data from the early primaries. He found not only that the Democratic electorate is getting more liberal, but that it is shrinking. Exit polls and vote totals in the early Democratic primary states find that the Democratic electorate is "much more liberal" than it was eight years ago.

More than two-thirds of voters in each of the first three Democratic primary states (Iowa, New Hampshire and Nevada) call themselves liberal. That share increased 14, 11 and 25 percentage points respectively from 2008.

Barone notes that this leftward trend isn't due to a surge of liberal voters into the Democratic electorate. Democrat turnout was down significantly in all three states, and self-identified liberals remained roughly steady in each of them compared to 2008.

Rather, it's mostly due, as Barone puts it, to "a flight of moderates and conservatives from Democratic contests." The number of moderates and conservatives plummeted 46 percent, 38 percent and 64 percent, respectively.

Barone concludes that the liberal polices promoted by Sanders and Clinton are leaving centrist and conservative Democrats on the sidelines or looking for other options.

This is the not the first or only study to arrive at such a finding. A study published last fall by a team of political scientists found that state Democratic parties are moving further to the left than state GOP parties are moving to the right.

This might explain why Gallup recently found that for the first time "red" states outnumber "blue" ones. Gallup found that 20 states are solidly red (meaning Republicans outnumbered Democrats there by at least 10 percentage points) and 14 that are solidly blue.

Not only is the Democratic Party shrinking and becoming more extreme, but Barone finds that the Republican base is expanding, in large part due to the addition of evangelical voters.

Vermont socialist Bernie Sanders' popularity and early primary success has fed the popular myth that demographic shifts and other changes in the electorate have produced a country more amenable to liberalism. But that's a false narrative.

Sure, there are issues on which the country is more liberal, such as same-sex marriage. But there are others on which it has moved in a conservative direction, including on gun rights, and many more on which the country remains divided. It is the Democratic Party, not the nation as a whole, that has become more liberal.

In a divided country, the Democrats' movement leftward risks alienating millions of voters who are unhappy with the state of politics and also dislike the agenda that today's Democrats offer.