Ours is a best-of-times, worst-of-times era for American liberalism. I've seen the contradictions up close in recent weeks.

From the progressive promised land of today's urban politics has come a procession of, um, open-minded candidates for city offices in Minneapolis and St. Paul, seeking endorsement from the Star Tribune Editorial Board.

A more shadowed liberal landscape was explored at a gathering of Democrats last weekend at the University of Minnesota, assembled to remember the 15th anniversary of the heartbreaking death of U.S. Sen. Paul Wellstone — and to ask how the buoyant, progressive populism Wellstone championed can have fallen so low as to be displaced by the snarling nationalistic populism of a certain "blue-collar billionaire" — and by Democratic defeats of historic proportions across the country (central cities notwithstanding).

Meanwhile, a new Pew Research Center report on our evolving political parties reveals transformations that suggest some explanations.

In the big cities, all bike lanes seem to be turning left, with the only debate being how far and fast to press the progressive vision at the local level. The economic distress of low-income populations, reaccelerating crime and troubled police-community relations rightly worry would-be mayors or City Council members. But few confess to fretting much about, say, property tax levels, or oppose any but the most extreme entries in a lengthy catalog of formidable business mandates on wages, work rules, rental regulations and more that the cities either have imposed or are considering.

Whatever this uncontested bluer-than-blue dominance of City Halls portends for the well-being of many large urban centers — similar regimes govern from Seattle to Chicago to Baltimore — the concentration of progressives in glittering emerald cities of the new global-tech economy may reflect a political problem for the left that author Thomas Frank diagnosed bluntly at the University of Minnesota last week.

Something of a pugnacious political pathologist, Frank excoriated Republicans in 2004 — in "What's the Matter with Kansas?" — for hypnotizing rural, blue-collar America with a "culture war" agenda of losing social causes while pushing big-business policies on trade, taxes and deregulation that do nothing to improve ordinary Americans' lives.

Early in 2016, Frank turned his political colonoscope on his own party. In "Listen, Liberal: Whatever Happened to the Party of the People?" he explained why the Democrats lost to Donald Trump — many months before the catastrophe actually occurred.

Frank's diagnosis is precisely that Emerald City Democrats have done all too well, utterly conquering the party over the past quarter-century or so — and causing it to lose both its connection and its commitment to its historic working-class base.

The Democrats have become the overeducated party of the "professional class," the "creative class," the "well-graduated," Frank says. Intoxicated with dreamy talk of "innovation" and "global competitiveness" and "creative clusters," Clintonian Democrats of recent decades stopped opposing trade and deregulation schemes that undermined broad-shouldered workers, stopped demanding a fairer distribution of wealth — and cozied up to monopolists from Wall Street to Silicon Valley.

Such elitist "globaloney" could only work for Democrats, Frank writes, "as long as Republicans did their part and adhered to free-market orthodoxy." But then came Donald "America First" Trump.

Frank focuses almost entirely on economic issues that have estranged the working class from the "creative class" — partly, no doubt, because it's on economics that Democrats may have grown too moderate for blue-collar America. But he conceded in our conversation at the U that cultural differences, too, divide trendy and traditional populists. Well-graduated Democrats, he says, too often disdain reconnecting with rural and blue-collar Americans they see as racists and homophobes, with bad taste besides.

Meanwhile, new polling data from Pew Research confirms that the ideological divide between Democrats and Republicans continues to grow wider. What may be more surprising is that Pew says the gap's increase seems mainly due to Democrats becoming more liberal, while Republicans have changed less.

Demographic shifts in the makeup of the parties tell a tale. In the 25 years since 1992, Pew reports, the overall American electorate (registered voters) has become notably less white and better educated. Both parties have changed in the same directions.

But the GOP has become slightly less white and slightly more educated, while Democrats have grown much less white and much more educated.

The result is that each party now looks a lot less like the overall electorate than it did a generation ago.

That our parties are becoming more racially defined is an uncomfortable but undeniable fact. Today Democrats (and Democratic-leaning voters) are only 57 percent white, down from 76 percent in 1992. The GOP's white support (again including leaners) fell only from 93 percent to 85 percent. (Today's electorate overall is 70 percent white.)

At least as transformative is that Democrats have become more likely to hold a college degree (at 36 percent) — than Republicans (30 percent). This is a major shift; a quarter-century ago, Republicans were the more educated party.

Combine those trends and you get a remarkable decline in the role non-college-educated whites play among Democratic voters. Fewer than one-third of Democrats and leaners today are such "working-class" white Americans, barely half the 59 percent of 25 years ago and well below their 45 percent presence in today's overall electorate.

And, yes, on many issues, from corporate profits to gay rights to the ability to get ahead through hard work, it is Democrats whose attitudes have changed the most. Consider just one hot-button issue: immigration.

In 1994, Pew reports, Republicans and Democrats had nearly identical (not very favorable) views on immigrants, with 30 and 32 percent, respectively, saying immigrants make America stronger. Attitudes warmed some in both parties and stayed nearly identical until around 2007, at which point Democrats underwent a drastic change of heart. Today fully 84 percent of Democrats and leaners believe immigrants strengthen America, while just 42 percent of Republicans feel that way.

Make no mistake, these trends spell potential trouble for the GOP, too, especially over time. As is often noted, America's long-term demographic trends likely favor the diverse Democratic coalition.

But for now, given how far and fast liberals have parted company from what remains a core American constituency, it's small wonder they don't feel quite at home outside their fortress cities.

D.J. Tice is at Doug.Tice@startribune.com.