(CNN) President Donald Trump's openly racist and xenophobic attacks on four Democratic House women of color , like his threatened immigration enforcement raids in major cities and the sweeping proposed new restrictions on asylum seekers that he announced Monday, underscores his transformation of the Republican Party into a coalition centered on the voters and places in America most hostile to immigration in particular and demographic change in general.

This latest flurry of activity continues the drive by Trump and other Republicans elected mostly from the parts of America least touched by immigration to impose a restrictionist agenda on migration over the nearly undivided opposition of Democrats elected by the areas where most immigrants, both undocumented and legal, actually live. Though greeted without complaint by Republicans in Congress, Trump's promised raids provoked astoundingly open resistance from the mayors of virtually every large American city , from New York and Los Angeles to Chicago and Houston.

Trump's divisive tweets opened an equally imposing divide between the parties. Democrats were unvarnished and united in flatly describing Trump's tweets as racist and nativist, words that elected officials have rarely applied so unabashedly to the remarks of a sitting president. Only a tiny trickle of Republicans that widened slightly as Monday progressed raised objections and the vast majority tried to avoid comment altogether. Sen. Lindsey Graham of South Carolina obliquely suggested Trump "should aim higher" but then compounded the President's slur by calling the Democrats "communists" who "hate our own country" and are "anti-America."

This week's stark divide on both fronts, coming immediately after battles that also polarized the parties over Trump's border detention policies and his failed effort to add a citizenship question to the 2020 census, crystallize how Trump is accelerating a long gestating shift in the axis of American politics from class interests to cultural attitudes.

As I've written before, attitudes toward demographic, cultural and economic change have become the central fault line between the parties. Republicans mobilize what I've called a "coalition of restoration" centered on older, blue-collar, evangelical and non-urban whites who polls show are uneasy or frightened about the fundamental demographic, cultural and even economic trends reshaping America in the 21st century.

Democrats counter with a competing "coalition of transformation" revolving around the groups -- young adults, minorities, singles, secular voters, and college-educated whites, mostly concentrated in large metropolitan areas -- who are most comfortable with the change.

"Clearly we're headed down a path where there is one party for older white Americans and then there's another party for people of color and immigrants," says Carlos Curbelo, a former Republican US representative who was defeated last fall in a heavily diverse Miami-area district. "And this is very dangerous. It divides our society in a dangerous way. It paralyzes our political system."

These trends trace their roots back all the way to the civil rights revolution in the 1960s and have significantly accelerated since the closely divided election of 2000. But Trump's open appeal to the portions of white America most uneasy about cultural and social change, from immigration to gay and transgender rights and the changing role of women , have elevated these trends to an entirely new level.

The result is that hardly any Republicans at any level now represent urban constituencies with the large immigrant populations that Trump has threatened with intensified ICE enforcement or demeaned with his calls for four liberal House Democratic women, three of whom were actually born in the US, to"go back" to where they came from before criticizing America.

"I don't see any serious plan or strategy to grow the party in urban America," said Curbelo, who was one of the few House Republicans to represent a seat with large populations of immigrant and non-white voters. "And I see very limited effort to grow the party among the Hispanic community which was a major priority during the George W. Bush years and even afterwards during the Obama presidency. That is now virtually non-existent."

Instead, Curbelo said, Trump "uses cities to intensify the culture war and agitate his base."

Trump's victory in 2016, and his consistent support in polls from about 40-45% of the population, shows there is a significant audience for his hard-edged message on immigration and demographic change more broadly. But there is also a clear cost. In effect, Trump's bruising racially-infused nationalism is forcing the GOP to trade support among younger voters for older ones; secular voters for the most religiously conservative, especially evangelical Christians; diverse voters for whites; white collar whites for blue-collar whites; and metro areas for non-metro areas.

Since Trump's emergence Republicans have consolidated their control of small-town, exurban and rural communities. But that has come with significant losses for the GOP inside metropolitan areas even in red states, like Texas and Georgia.

The trade Trump is imposing on the GOP was apparent in 2016 and enormously intensified in 2018.

In 2018 House races, Republicans suffered only very modest losses outside of metropolitan area districts. And they gained three Senate seats in states with large populations of white voters who are rural, blue-collar, or evangelical Christians: North Dakota, Indiana and Missouri. But the party was routed in metropolitan House seats that contained significant populations of minorities, immigrants, singles, college-educated white voters, or all of the above. After sweeping losses in suburban districts from coast to coast, the GOP under Trump has been almost completely exiled from the dynamic metropolitan areas that account for the nation's vast majority of job growth and economic output

Democrats now hold over four-fifths of the House seats where minorities exceed their share of the national population and nearly 9 in 10 of the House seats with more foreign-born residents than average, according to a CNN analysis of census data. In the Senate, Democrats partially offset the Republican gains in older and rural Midwestern states by adding seats in the diverse, younger, rapidly growing Sunbelt battlegrounds of Arizona and Nevada. The result is that after the 2018 election, Democrats now hold 32 of the 40 Senate seats in the 20 states with the highest share of immigrants in their population while Republicans hold 45 of the 60 in the 30 states with the fewest. In 2020, the top two Democratic Senate pick-up opportuntiies are among the top 20 immigration states -- Arizona and Colorado, with Georgia, another high-ranking state, presenting a more difficult chance. Democrats are also targeting about a dozen of the GOP House members remaining in high-immigrant seats.

Because undocumented immigrants tend to flow largely toward communities with large existing immigrant communities, that means the places most threatened by Trump's threat to increase ICE enforcement are almost all places that have already demonstrated hostility to him and the party he is reshaping in his image.

The non-partisan Migration Policy Institute estimates that there are at least 70,000 undocumented immigrants in 34 US counties; cumulatively those counties account for about 5.6 million undocumented immigrants, about half of the estimated US total. (The top 10 counties alone, all of them major metropolitan areas, account for nearly one-third of the total undocumented population.) In 2016, Trump lost 31 of those 34 counties and in 2018 two of those he carried -- Maricopa, around Phoenix in Arizona, and Tarrant, centered on Fort Worth in Texas -- broke for the Democrats in Senate races.

Trump and some of his supporters have falsely claimed that voter fraud allowed undocumented immigrants to vote in these big urban places contributed to his losses in some states. It is, however, accurate to say that acceptance of an undocumented population in those communities is part of the fabric of attitudes that have made them so hostile to Trump.

Those public attitudes help explain why the mayors of almost all of the nation's largest cities -- the very places where the undocumented population is concentrated -- felt so comfortable displaying public resistance to Trump's enforcement initiative. Mayors Bill de Blasio of New York and Eric Garcetti of Los Angeles, the nation's two largest cities, joined many other mayors in publicly offering legal help to undocumented residents facing ICE enforcement. Atlanta Mayor Keisha Lance Bottoms told CNN's Poppy Harlow last Friday that Atlanta has "closed our city detention centers to ICE because we don't want to be complicit in family separation."

In an interview, Providence, Rhode Island, Mayor Jorge Elorza, the co-chair of the immigration reform task force at the US Conference of Mayors, captured the ferocity of the resistance from mayors to the threatened ICE raids. He called them "blatantly racist" and said Trump revealed their political intent with his tweets telegraphing the apparent operation. "If it was about executing a public policy you wouldn't give the heads up to these folks that these round ups and raids are coming," Elorza said. "The goal...is to stoke fear in the broader immigrant community and to do it in a way that feeds red meat to their political base."

Elorza said almost all mayors consider such hardline enforcement tactics counterproductive to public safety because they strain relations between immigrant communities and law enforcement. "We want whoever witnessed (a crime) to feel as comfortable as possible coming forward talking to the police," said Elorza, the US-born son of undocumented immigrants from Guatemala. "If people are afraid to come to the police, they are less likely to speak up even they are witnesses."

Muzaffar Chishti, director of the Migration Policy Institute's New York office, said in an interview that Trump's hardline approach is counterproductive even to his stated goal of increasing deportations. The reason, Chishti says, is that while many cities chafed under former President Barack Obama's deportation actions, they have been completely alienated by Trump's brusque immigration policies and language (including his attempts to cut federal policing aid to so-called sanctuary cities that limit cooperation with federal immigration enforcement). And cooperation from cities, Chishti says, is essential to removing large numbers of undocumented immigrants because three-fourths of those who are eventually deported are originally arrested not on immigration charges, but for other offenses and then found by ICE once they enter the criminal justice system.

"If you want large numbers (of deportations) you have to rely on...states and localities, because our criminal justice system is state and local not federal," he says. "Therefore you need their cooperation. And if they are not cooperating you are not going to get big numbers."

Yet within city governments there is a widespread sense that Trump's immigration agenda is essentially an effort by a Republican coalition centered primarily on the parts of America with fewest immigrants to impose their values and prejudices on the parts of America with the most.

Trump "has been able to convince folks that their way of life has been impacted primarily by the presence of undocumented immigrants in this country and I think that that message resonates more than anywhere else with the communities that just don't have close contact with them," Elorza said. "I personally live in a community where I know for a fact there are undocumented immigrants around. I see them. And if you get to know them you see they are not a threat to you. When you are not exposed to them you are more susceptible to buying this (negative) narrative, because you have the President of the United States telling you this is the case."

Conversely, Curbelo says he sees signs that too many Democrats are abandoning the hope of forging connections in less diverse, less urban areas generally more skeptical of immigrants. "Obviously Republicans are not doing enough to change (the divide) and frankly Democrats aren't either," he says. "You hear some Democrats say we don't want a white presidential candidate; that's just as improper and scandalous. The bases of each respective party have too much of a gravitational pull."

Trump's unrelentingly divisive agenda and language -- and the sharp Democratic response it has generated -- seems guaranteed in the 2020 election to widen the chasm between diverse, white-collar, immigrant-friendly urban America, where opposition to the President is centered, and his strongholds in preponderantly white, blue-collar, heavily Christian, non-urban America.

This week's repeated use of openly racist language from the White House -- like the new policy battles over ICE enforcement and asylum seekers, and the earlier struggles over Trump proposals to measure citizenship on the census, build a border wall, separate children from parents at the border, punish "sanctuary cities," and slash legal immigration by the largest amounts since the 1920s -- show how committed the President is to mobilizing his "coalition of restoration" even at the price of inflaming the Democrats' "coalition of transformation" and potentially alienating swing voters.

The racially incendiary conflicts of the past few days have provided perhaps the clearest preview yet of what's approaching as the places that represent what America is becoming square off against the places that reflect what it has been in next year's epic struggle for control of the nation's direction.