Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Senate GOP aims to confirm Trump court pick by Oct. 29: report Trump argues full Supreme Court needed to settle potential election disputes MORE (R-Ky.) said on Thursday that the midterm elections will be "very challenging" for Republicans, predicting that both chambers are in play.

"I think the safest place to be is just to say that this is going to be a very challenging election, and I don’t think we know in May ... whether it’s Category 3, 4 or 5," he told The Washington Post.

He added that, historically, the party in power loses seats during off-year elections.

“It’s pretty hard to deny the history of off-year elections, particularly off-year elections two years into the first term,” McConnell said.

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Though control of the House is widely considered to be in play heading into November, Republicans face a more favorable map in their quest to keep control of the Senate.

Republicans have a narrow 51-49 majority in the chamber and face a slate of nasty primary fights.

But Democrats are defending roughly two dozen seats in November, including several in red and purple states won by President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE in 2016. Trump, during his closed-door meeting with Republicans this week, specifically name-checked Democratic Sens. Joe Donnelly Joseph (Joe) Simon DonnellyTrump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court Momentum growing among Republicans for Supreme Court vote before Election Day MORE (Ind.) and Joe Manchin Joseph (Joe) ManchinThe Hill's Morning Report - Sponsored by Facebook - Trump, GOP allies prepare for SCOTUS nomination this week Trump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court MORE (W.Va.).

McConnell, however, told the Post that control of the Senate could be determined, in part, by the outcome of battles for seats currently held by Republicans.

In addition to Montana, North Dakota, Missouri, Indiana, West Virginia and Florida, where Republicans want to unseat Democratic incumbents, McConnell also pointed to the Senate battles in Arizona, Nevada and Tennessee.

GOP Sen. Dean Heller Dean Arthur HellerOn The Trail: Democrats plan to hammer Trump on Social Security, Medicare Lobbying World Democrats spend big to put Senate in play MORE is running for reelection in Nevada while GOP Sens. Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (Tenn.) and Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (Ariz.) are retiring, sparking fights for who will replace them.

"By any objective standard, those are the seats that are likely to be in play,” McConnell told the Post.

The Senate GOP leader did not, however, mention Ohio, Pennsylvania and Wisconsin, where Democratic Sens. Sherrod Brown Sherrod Campbell BrownSenate Democrats release report alleging Trump admin undermined fair housing policies Bipartisan praise pours in after Ginsburg's death Emboldened Democrats haggle over 2021 agenda MORE, Bob Casey Robert (Bob) Patrick CaseySecond GOP senator to quarantine after exposure to coronavirus GAO report finds brokers offered false info on coverage for pre-existing conditions Catholic group launches .7M campaign against Biden targeting swing-state voters MORE Jr. and Tammy Baldwin Tammy Suzanne BaldwinKeep teachers in the classroom Cher raised million for Biden campaign at LGBTQ-themed fundraiser Democrats seek balance in backing protests, condemning violence MORE, respectively, are running for reelection in states won by Trump.