Congress is about to get a shake-up. Here's what's coming with new census data.

The Census Bureau is set to release the long-awaited data states need to draw new voting maps Thursday, kicking off what advocates fear will be the most hectic, contentious redistricting cycle yet.

The detailed, local-level population results arrive months behind schedule thanks to Covid-related delays, which means the notoriously complex and sometimes secretive process of determining congressional district boundaries will happen more quickly as states try to finish before the end of the year. It's typically a once-a-decade undertaking coinciding with the decennial census, a population count that decides everything from congressional representation to the distribution of federal aid.

Redistricting has the power to shape elections for years. But this cycle, experts and voting rights advocates agreed, the stakes are higher than ever. New maps drawn by state Republicans could gerrymander Democrats out of their slim majority in the House, results of the 2022 midterms aside, experts said. It's also the first time the redistricting process is occurring since the Supreme Court gutted key federal protections against discriminatory maps in 2013 while giving a green light to partisan gerrymandering in 2019, leaving advocates fearful that the boundaries could significantly dilute the political power of people of color even as minorities are driving the country's population growth.

"From the standpoint of voters of color in the South, a train is headed down the tracks, and we've been able to see this coming for a long time. The reality is in places of the South you cannot do a partisan gerrymander without targeting voters of colors," said Michael Li, a redistricting expert and senior counsel at the Brennan Center for Justice at New York University School of Law. "Because of residential segregation, it's easier to break apart or pack together communities of color to move the dial."

What is gerrymandering?

Gerrymandering, the act of manipulating boundary lines to favor one party or class of people, is as old as American politics. But technology and improved data have made it possible for lawmakers to draw district maps with increasing precision. Experts and critics argue that letting legislators draw district lines allows them to choose their own voters, while the people doing the gerrymandering tend to argue that voters elected them and gave them the power to do as they see fit.

And while both parties have historically been guilty of gerrymandering, Republicans invested heavily in campaigns for the state legislatures ahead of the last cycle and won down-ballot races that helped them secure control of the process. "He who controls redistricting can control Congress," Republican strategist Karl Rove wrote in spring 2010, outlining the strategy in an opinion article for The Wall Street Journal. The maps Republicans drew the next year gave the GOP a significant advantage in the last decade. An Associated Press analysis found that in the 2016 election, Republicans won as many as 22 extra seats in the House over what would have been expected based on the average vote share in congressional districts across the country.

In this year's redistricting cycle, Republicans will again control much of the process. GOP legislators are charged with drawing 187 House districts compared to Democratic legislators, who control the drawing of 75 districts, according to an analysis by Kyle Kondik of the University of Virginia's Center for Politics.

The 173 other boundaries are drawn by states with split control, independent commissions or no maps at all because they are single-district states. That is in part because voters in some states have handed control of their redistricting processes to commissions, arguing that voters or appointed commissioners can draw better district lines than politicians who have vested interests in drawing maps that help them keep power.

In another opinion article for The Wall Street Journal this year, Rove argued that Democrats were boosting themselves in drawing maps even as they decried gerrymandering.

"The truth is both parties use redistricting to enhance their position. However, only one pretends to be holier than thou in the process," he said.

What are the census data expected to show, and what's next in the process?

The data will show — in the most precise way possible — where people live, detailing the ethnic, racial and voting-age makeup of neighborhoods.

They're expected to show that the nation is fast diversifying, while the share of white voters — and potentially even the population of white people — is shrinking.

The data will be handed to map drawers — the state legislatures, the independent commissions — who then set out to create equally sized House districts, so that all 435 members represent about the same number of voters.

In April, the Census Bureau released state population totals that determine each state's number of House seats, with just seven seats moving among 13 states — the smallest shift since the current congressional apportionment model was adopted in the 1940s.

Texas was the biggest winner, gaining two House seats. Colorado, Montana, Oregon, Florida and North Carolina gained one seat apiece.

The losses were concentrated in the industrial Midwest, where Illinois, Michigan, Pennsylvania, West Virginia and Ohio each lost a seat. The Democratic strongholds California and New York also each lost a seat.

The dataset released Thursday is expected to reinforce a known trend: that Hispanics have been driving the country's growth over the past decade. They are the largest racial and ethnic minority in the country, but that hasn't automatically translated into more political power, in part because of gerrymandering. And advocates fear that maintaining the trend could continue to dilute Latinos' political power.

Latino lawmakers and others have expressed fear that the results released Thursday will indicate that the census has significantly undercounted the Latino population, as it has in past years. Former President Donald Trump's failed attempts to include a citizenship question on the census and to exclude people without legal permission from being in the U.S. in the results made some afraid to fill out the survey, NBC News has reported.

Activists in communities of color say they will try to mobilize their voters to get involved in the process, urging fair boundaries and preparing to lobby against what they consider unfair maps.

Fenika Miller, an activist from Houston County, Georgia, who works with Black Voters Matter, a nonprofit advocacy group, said the 2011 redistricting helped damage her community by breaking up Black communities into multiple districts.

"You're hard-pressed to find that Black people have been represented fairly here. It's hard for people to believe that we can have more progressive, fair and diverse representation," she said. "We have to educate folks to help them understand how being drawn out of power negatively impacts our communities and quality of life."

What's different about this cycle?

The loss of Section 5 of the Voting Rights Act, which the Supreme Court gutted in 2013, is likely to lead to the most significant change this year from past redistricting cycles, activists and experts said. The provision had required states to prove to the Justice Department that their district maps wouldn't discriminate against voters of color.

"There's nothing that prevents states from being really aggressive and daring a court to strike it down," said Li of the Brennan Center for Justice. "Before, you knew there was a cop on the beat, so you modified your behavior a little bit. Now, without a cop on the block, you can push old ladies around, you can target communities of color, you can do whatever you want, and maybe the cops will arrive after someone calls for them, but maybe they won't."

The ruling is a major reason voting rights advocates have pushed for federal voting legislation that seeks to ban partisan gerrymandering. The proposal is stalled in the Senate.

In addition, advocates said, a more recent Supreme Court ruling that said federal courts could not consider partisan gerrymander claims offered Republicans a ready defense against those who might argue that a map is discriminatory. There's a strong overlap between race and partisanship.

Jon Greenbaum, chief counsel and senior deputy director of the Lawyers' Committee for Civil Rights Under Law, a nonprofit advocacy group, said partisan gerrymandering was of particular concern to him in Georgia, where Black voters were key to President Joe Biden's win last year and to the outcomes of the Senate runoffs in January that handed Democrats control of the Senate. Republicans control all three branches of state government, along with the redistricting process.

Greenbaum, one of the authors of a recent report by the Lawyers' Committee outlining the risks of partisan gerrymandering in the state, noted that Georgia's voter registration form asks voters to list their race, not their party.

"I'm sure you're going to hear from the map drawers in Georgia: partisanship, partisanship, partisanship, partisanship," he said. "They'll avoid using the word 'race' as much as they can get away with."