After the Trump administration attacked Canada's prime minister over trade policy, dissident Sen. Jeff Flake beseeched fellow Republicans: "This is not who we are. This cannot be our party."

With similar language, other Republicans objected to President Donald Trump's hard-line policies separating children from their illegal immigrant parents. Yet before Trump backed down through executive order today, the GOP Congress had not blocked him on either front — despite worldwide condemnation layered on top of financial market turmoil over trade.

The reason is one Republicans like Flake won't find reassuring. Within the GOP, "who we are" is not "who we were."

In 1986, when Flake graduated from college, conservative icon Ronald Reagan dominated American politics. That year, the Republican president negotiated the free trade agreement with Canada that eventually became NAFTA, and joined Congress to enact a bipartisan overhaul of America's immigration system.

Since then, the composition of both parties has substantially changed. For Democrats, that brought an infusion of non-whites, whites with college degrees, and younger voters; for Republicans, surging numbers of less-educated, evangelical and older whites.

Pew Research Center has charted trends in party identification over the last generation. From a distance, little appears to have changed: In 1992, self-described Democrats outnumbered Republicans by seven percentage points, the same edge they held 25 years later.

But up close, the data show how different those Republicans and Democrats are.

In 1992, when Bill Clinton won the presidency, whites represented 9 in 10 voters; by 2016, when Hillary Clinton lost it, whites were 7 in 10. That growing non-white constituency — Asian, Latino and African-American — swelled Democratic ranks.

One big chunk of white voters moved to join them. In 1994, just 38 percent of white college graduates called themselves Democrats; by 2017, Pew reported, a 53-percent majority did.

Republicans compensated by attracting more whites without college degrees. That long-term trend accelerated after Barack Obama became the nation's first African-American president.

In 2008, as Obama sought the White House, non-college whites split evenly between the two parties. By 2017, Pew found, they tilted strongly toward Republicans, 56 percent to 37 percent.

An overlapping Obama-era shift occurred among older voters. In 2008, members of the "Silent Generation" born between 1925 and 1945 leaned slightly toward Democrats, 48 percent to 41 percent; by 2017, Silent Generation voters spoke for Republicans by a margin of 52 percent to 43 percent.

Republicans turned an eight-percentage-point 2008 deficit among white Catholics into a 14-percentage-point Republican advantage. The large GOP edge among white evangelicals (64 percent to 28 percent in 2008) grew even larger (77 percent to 18 percent in 2017).

Trump did not create those trends. He won the Republican nomination, and then the White House, by capitalizing on them.

That explains his insistence on policies old-school Republicans find offensive, and the refusal of Congress to intercede. Both advance the priorities of the Republicans who remain most loyal to him, and rule party primaries.

Dubbed "American Preservationists" by Cato Institute analyst Emily Ekins in a June 2017 study, Trump's original core constituency have relatively low levels of education and income. They fear the loss of Social Security and Medicare benefits.

They dislike free-trade deals, think of "real Americans" as native-born Christians, feel more negatively toward minorities than other Americans do and complain of discrimination against whites. They oppose both legal and illegal immigration.

Their attitudes match Trump's pledge to protect existing old-age benefits, his talk of shredding trade deals, his declaration that "Christmas is back," his attacks on African American athletes protesting racial injustice and his border crackdown. Other GOP leaders, to the extent they disagree, fear defying them.

Their congressional majorities are at risk. In a Quinnipiac University poll released today, Democrats lead among blacks for the House by a margin of 76 percentage points, among Hispanics by 27 percentage points, and among white college graduates by 10 percentage points.

Yet Republicans remain competitive overall for holding the House. They trail Democrats by 6-percentage-point spread — 49 percent to 43 percent — thanks in part to virtually splitting the vote among voters over age 50.

What powers GOP hopes most, however, is their lopsided 59 percent to 32 percent lead among whites who haven't graduated from college. For purposes of elections this November, that is who Republicans are.