SHAWNEE, Kan. — One week before Election Day, Democrats and Republicans across the country see an expanding battlefield for the House majority that hints at a tumultuous and unsettled environment rocked by political violence and ethnic strife.

The number of seats in play has ballooned, with Democrats seeking to extend the playing field in the hope that a blue wave will develop even in districts across the country that voted more heavily in 2016 for President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE.

The largest outside groups backing Democrats have begun sending mail to districts held by Reps. John Carter John Rice CarterDonna Imam wins Democratic runoff to face Rep. John Carter House panel advances bill banning construction on bases with Confederate names Democrats see victory in Trump culture war MORE (R-Texas), Lamar Smith Lamar Seeligson SmithOVERNIGHT ENERGY: Cheney asks DOJ to probe environmental groups | Kudlow: 'No sector worse hurt than energy' during pandemic | Trump pledges 'no politics' in Pebble Mine review Cheney asks DOJ to probe environmental groups How effective are protests and riots for changing America? MORE (R-Texas), Vern Buchanan Vernon Gale BuchananMORE (R-Fla.) and Jackie Walorski Jacqueline (Jackie) R. WalorskiLawmakers press CDC for guidance on celebrating Halloween during pandemic More than 100 lawmakers urge IRS to resolve stimulus payment issues Scaled-back Pride Month poses challenges for fundraising, outreach MORE (R-Ind.) and in a seat formerly held by Republican Ron DeSantis Ron DeSantisOvernight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Florida to lift all COVID-19 restrictions on restaurants, bars MORE in Florida.

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That spending represents an against-the-odds bid to expand the number of opportunities Democrats have to gain seats, according to party strategists familiar with the moves. Most of the districts are the kind of seats that are only likely to be won by Democrats if the wave is big, but the spending points to an underlying confidence for the party.

Republicans, for their part, discount the notion that a real national wave is in the offing, pointing to Trump’s approval rating, which has risen somewhat, and poll numbers that show the Democratic advantage in the so-called generic ballot matchup stagnating or even shrinking.

But to judge by deeds instead of words, even Republicans see a need to shore up vulnerable incumbents and seats once deemed safe.

The National Republican Congressional Committee on Monday moved to purchase late advertising time in districts held by Reps. Jaime Herrera Beutler Jaime Lynn Herrera BeutlerCentrist Democrats 'strongly considering' discharge petition on GOP PPP bill This week: House returns for pre-election sprint GOP Rep. Jaime Herrera Beutler advances in Washington primary MORE (R-Wash.) and Mark Sanford Mark SanfordOn The Money: Business world braces for blue sweep | Federal Reserve chief to outline plans for inflation, economy | Meadows 'not optimistic' about stalemate on coronavirus deal Trump critic Sanford forms anti-debt advocacy group Republicans officially renominate Trump for president MORE (R-S.C.), who lost his bid for re-nomination in the spring.

The party is even spending on behalf of Rep. Will Hurd William Ballard HurdHillicon Valley: Oracle confirms deal with TikTok to be 'trusted technology provider' | QAnon spreads across globe, shadowing COVID-19 | VA hit by data breach impacting 46,000 veterans House approves bill to secure internet-connected federal devices against cyber threats House Democrats' campaign arm reserves .6M in ads in competitive districts MORE (R-Texas), an incumbent who once looked like such a safe bet for reelection that Republicans canceled their planned advertising spending there.

Hanging over the final week of the campaign is the mass shooting at a Pittsburgh synagogue — the deadliest single incident of violence against Jewish people in U.S. history — as well as the string of package bombings sent to prominent Democrats.

The violence has left much of the country on edge while underlining the stark polarization in politics that seems worse than any period since at least the Vietnam-era 1960s.

It has also added an unpredictable tinge to the midterm campaign’s last days.

Trump, who railed against the “fake news” media on Monday and warned of an “invasion” from the migrant caravan in Mexico traveling toward the U.S. border, is set to travel to Pittsburgh on Tuesday.

The two parties fighting for control of the House of Representatives are battling across huge swaths of the country, from the North Woods of Maine to the sunny coasts of Southern California, from a suburban Seattle district that includes Mt. Rainier to the conservative Florida Gulf Coast.

For months, Democrats have focused their attention on Republican-held districts in suburban areas, where they hope voters punish an unpopular president’s party. That includes Rep. Kevin Yoder Kevin Wayne YoderBottom line Amanda Adkins wins GOP primary to challenge Rep. Sharice Davids Sharice Davids to vote for Trump impeachment articles: 'The facts are uncontested' MORE’s (R-Kan.) district, centered in Kansas City, Kan., where Democratic nominee Hillary Clinton Hillary Diane Rodham ClintonThe Memo: Trump furor stokes fears of unrest Bloomberg rolls out M ad buy to boost Biden in Florida Hillicon Valley: Productivity, fatigue, cybersecurity emerge as top concerns amid pandemic | Facebook critics launch alternative oversight board | Google to temporarily bar election ads after polls close MORE won a plurality of the vote in the 2016 presidential election and where voters said they were keenly aware of the choice they faced.

“It’s hard to find an issue that isn’t big,” said Deanna Bucko, after she cast her ballot for Yoder at an early voting station in this suburb of Kansas City.

Democrats have focused much of their campaign on health care, while Republicans have increasingly adopted Trump’s attacks, particularly on immigration.

Many, though not all, Republicans, far from distancing themselves from Trump, have tied themselves to him — and even some members who have taken care to cultivate independent images, like Yoder, have begun to embrace Trump’s dark warnings about the migrant caravan headed toward the southern border.

“I think everyone should be talking about it. It’s a really scary thing. And the word caravan, you can use that all day long, but it truly looks like an invasion of our country,” Lara Trump, a senior advisor to the president’s reelection campaign and Eric Trump Eric Frederick TrumpJudge orders Eric Trump to comply with New York AG's subpoena before Election Day Eric Trump uses misleading clip to blast Biden for using teleprompter Melania Trump: Ginsburg's 'spirit will live on in all she has inspired' MORE's wife, said in an interview.

To some Democrats, the Republican effort to find a message that works reminds them of 2010, when the GOP reclaimed the majority virtually entirely because of anger at the slow economic recovery and opposition to the Affordable Care Act.

“The cycle definitely feels like 2010 in reverse,” said Shripal Shah, a Democratic strategist who worked at the Democratic Congressional Campaign Committee in 2010. “They went from running on a tax plan and daring the opposition to oppose it, then trying to localize inherently national races, to where we are now, scorched-earth negative, and hoping for the best.”

Both parties are racing to spend more money in a significant number of House districts far astray of the typical battleground districts.

The largest super PAC on the Republican side has spent recently in districts held by Reps. Scott Taylor Scott William TaylorBottom line Bottom line Republican Scott Taylor wins Virginia primary, to face Elaine Luria in rematch MORE (R-Va.) and Ted Budd Theodore (Ted) Paul BuddHouse Dems introduce bill to require masks on planes and in airports Bipartisan bill introduced to require TSA to take temperature checks How to combat substance abuse during COVID-19 MORE (R-N.C.), neither of whom were seen as particularly vulnerable as the cycle began.

In the final week of the race, the largest Democratic groups are spending money in 64 media markets around the country, according to sources watching the advertising market. Republican groups are spending in 58 markets.

Republicans have been taken aback by the enthusiasm on the Democratic side, one that shows up in campaign finance reports made in the final weeks of the race. Since Jan. 1, Democrats and their supporters have outspent Republican forces by a margin of more than $125 million.

In some of the most hotly contested media markets, like Los Angeles, New York City and Washington, D.C., Democratic spending is twice as high as Republican spending. In virtually every market, Democrats are outspending Republicans on television by millions of dollars.

“It obviously looks slightly better on the Democrat side,” Lara Trump conceded.

CORRECTION:A previous version of this story incorrectly listed Republican spending in Wisconsin. The source of that information, Medium Buying, has corrected their information.