ATLANTA >> In 1963, Martin Luther King, Jr. had a dream that, to the joy of millions of African-Americans, Barack Obama redeemed by winning the presidency.

As the youngest speaker at that March on Washington gathering, John Lewis identified another dream. It, too, has been redeemed by the American political system.

But the blessing has been decidedly mixed.

On that sweltering August day, Lewis, the 23-year-old champion of voting rights, lamented the absence of an unequivocal “party of principles” from the political scene. “The party of Kennedy is also the party of Eastland,” Lewis said. “The party of Javits is also the party of Goldwater.”

He was describing the disparate ideological blends that characterized both parties at that time. Democrats spanned the distance from the liberal young President John F. Kennedy, then gingerly trying to advance civil rights, to the conservative Sen. James O. Eastland of Mississippi, a segregationist aiming to thwart him. Republicans stretched from Sen. Jacob K. Javits of New York, a Kennedy ally on the issue, to Sen. Barry M. Goldwater of Arizona, who opposed the landmark Civil Rights Act that passed the next year.

In the half-century since, the unalloyed “party of principles” Lewis yearned for has come to pass. Present-day Democrats, including those in the House of Representatives, where Lewis has represented Georgia for nearly 30 years, uniformly share Lewis’ vision of racial progressivism.

Present-day Republicans have long since abandoned Goldwater’s opposition to the Civil Rights Act. Yet the Arizonan’s deep-rooted conservatism, advanced later by Ronald Reagan and Newt Gingrich, now defines the party on issues from economics to voting rights.

As a result, racial and ideological divisions that have always characterized American politics now coincide precisely with partisan ones. “Congress has become so, so partisan,” Lewis, said in an interview from his hometown, Atlanta. “I’m not sure whether it’s better or not.”

In the 2016 presidential race, Democrats hope their domination of the growing constituency of nonwhite voters offsets public discontent over stagnant incomes and foreign threats. Republicans, overwhelmingly reliant on whites, have seen Donald J. Trump dominate their nomination contest by condemning many Mexican immigrants as criminals and proposing a temporary ban on Muslims entering the United States.

Lewis sees Trump as a modern-day version of George Wallace, the onetime Democrat and governor of Alabama who made his national reputation in the 1960s fighting integration. Like Wallace, he explained, Trump is simply responding to incentives the political landscape has provided him.

“It’s a reasonable comparison,” said Lewis, now 75. “See, I don’t think Wallace believed in all that stuff he was preaching. I think Wallace said a lot of stuff just to get ahead.

“I don’t think Trump really believes in all this stuff,” the veteran lawmaker added. “But he thinks this would be his ticket to the White House — at least to get the Republican nomination.”

Lewis says his friends across the aisle in Congress fear the rawness of Trump’s appeal, at a time they desperately need more black and Hispanic votes, and worry it could produce “the destruction of the Republican Party.” Lewis shares their hope that the new, young speaker, Paul D. Ryan, can offer a powerful counterweight by seeking to broaden his party’s constituency using issues of economic opportunity.

“I do think Paul Ryan is sincere,” Lewis said. “It is my hope, for the sake of the country and for the two-party system, that’s he’s able to do it.”

In one way, the polarization of American politics since the 1963 protest has flipped the script. Back then, Lewis complained that government was a den of “immoral compromises.” Today, outraged Tea Party Republicans say the same thing, complaining that political correctness prevents their leaders from doing the right thing.

“I understand their feeling,” Lewis said. “But I don’t agree with them. We come from two different worlds.”

© 2016 The New York Times Company