President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE and Republicans have made illegal immigration a central issue in the homestretch to the 2018 midterm elections, setting up a showdown over the U.S.-Mexico border in December.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellDemocratic senator to party: 'A little message discipline wouldn't kill us' House to vote on resolution affirming peaceful transition of power Republican lawyers brush off Trump's election comments MORE (R-Ky.) and Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) forestalled a fight over Trump’s border wall before the election by punting consideration of the Homeland Security appropriations bill until the lame-duck session.

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When lawmakers return, they won’t be able to avoid a fight over the spending measure, as funds for the Department of Homeland Security will run out on Dec. 7. But how it plays out could be determined by what happens on Nov. 6.

If it is a good day for Democrats, there may be little reason for the party to bend on Trump’s wall — even for a deal that provides a path to citizenship for “Dreamers,” people who came to the United States illegally as children.

House Minority Leader Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight 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 Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.), who could be the Speaker-in-waiting if Democrats retake the House, said last week that she isn’t interested in negotiating with Trump on the wall.

Senate Minority Leader Charles Schumer Chuck SchumerPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' 3 reasons why Biden is misreading the politics of court packing Cruz blocks amended resolution honoring Ginsburg over language about her dying wish MORE’s (D-N.Y.) office declined to comment on what his posture would be on the border wall after the elections.

If Democrats do not meet their expectations on Election Day, however, some think that Trump could have leverage.

“There will be a lot of pressure,” said Brian Darling, a former Republican Senate aide.

If Republicans do better than expected, he predicted that “Democrats are going to be despondent, and I think you will see them give up and give President Trump his border wall.”

What’s clear for the moment is that the White House is doing everything it can to make the next two weeks about immigration as Trump goes into overdrive to bring out his political base and protect GOP majorities in the House and Senate.

Trump is increasingly focusing attention on a “caravan” of about 7,000 immigrants who have traveled from Guatemala and Honduras and intend to reach the U.S. border.

While the caravan is roughly 1,000 miles from the U.S. border and is traveling mostly by foot, Trump has highlighted the group as a national security threat.

“In that caravan, you have some very bad people,” Trump said at a Monday rally in Houston while a raucous crowd chanted “build that wall.”

He called the caravan an “assault on our country” and suggested that “Democrats had something to do with it.” He added: “We need a wall built fast.”

Trump has talked repeatedly of people from the Middle East being a part of the caravan without providing any evidence.

In remarks to reporters from the Oval Office on Tuesday, Trump acknowledged the lack of proof.

“There’s no proof of anything,” he said in response to questions pressing him about how he knew of Middle Easterners in the caravan, while adding that “there very well could be.”

Vice President Pence has also played up the caravan as a threat, stating twice on Tuesday that it was “inconceivable” that the group did not include people from the Middle East while again offering no concrete proof.

The focus on immigration coupled with a series of other factors, including Trump’s rising approval rating, fallout from the fight over Supreme Court Justice Brett Kavanaugh Brett Michael KavanaughTrump plans to pick Amy Coney Barrett to replace Ginsburg on court Collins trails challenger by 4 points in Maine Senate race: poll SCOTUS confirmation in the last month of a close election? Ugly MORE’s confirmation and a growing economy, appears to be improving the GOP’s midterm chances, particularly in the Senate, where a number of races are playing out in red states.

A new Montana Television Network–Montana State University poll released Monday showed Sen. Jon Tester Jonathan (Jon) TesterDemocrats shoot down talk of expanding Supreme Court Pence seeks to boost Daines in critical Montana Senate race This World Suicide Prevention Day, let's recommit to protecting the lives of our veterans MORE (D-Mont.) — who seemed on safe ground earlier this year — with only a 3-point lead on his opponent.

A separate Missouri Scout poll conducted last week showed Sen. Claire McCaskill Claire Conner McCaskillMomentum growing among Republicans for Supreme Court vote before Election Day Democratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally MORE (D-Mo.) trailing her opponent by 1 point.

A new campaign ad launched Tuesday by the Senate Leadership Fund, a super PAC affiliated with McConnell, is hitting both senators over their votes on so-called sanctuary cities and illegal immigration.

Earlier this year, polls showed that Democrats were significantly more fired up than Republicans to vote.

Now there is some evidence that is changing.

Traditional Republican voters have turned out for early voting in greater numbers than Democratic-leaning voters in several key Senate battleground states: Arizona, Florida, Indiana, Montana, Tennessee and Texas, according to NBC News.

All of those states are hosting competitive Senate races in November.

Democrats remain favored to win the House, where they need to gain 23 seats on Election Day to retake the majority. The nonpartisan Cook Political Report on Tuesday announced it was moving eight more House races toward Democrats, while it moved two toward the GOP.

Ben Barnes, the former Democratic lieutenant governor of Texas, where Sen. Ted Cruz Rafael (Ted) Edward CruzCrenshaw looms large as Democrats look to flip Texas House seat SCOTUS confirmation in the last month of a close election? Ugly The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' MORE (R) is battling a tougher-than-expected challenge from Rep. Beto O’Rourke (D), says illegal immigration and the migrant caravan is “a good scare tactic,” especially in states that don’t understand the issue that well.

Some Democratic strategists, however, suggest the GOP and Trump could still end up losing with their rhetoric on immigration.

“As the country becomes browner when you look at 51 percent of all immigrants come from Mexico or Latin America, I really think at some point it’s going to become a huge Achilles’ heel for the Republicans,” said Steve Jarding, a Democratic strategist and former adviser to several Democratic senators from conservative-leaning states.