Pollster Dan Cox in an interview that aired Tuesday on "What America's Thinking" said that the Senate midterm map for Democrats is "historically difficult" this year.

"The map was never that favorable to Democrats to begin with," Cox, research director at the Public Religion Research Institute, told Hill.TV's Joe Concha. "It was a historically difficult map for them in places like Missouri, Arizona, North Dakota. They're trying to compete in places like Georgia and Texas, but those are kind of longshots."

"If you look at Texas, in particular, there has been so much tension on this race, but if you look at the polling, every statewide race, the Republican is leading," he continued.

While Democrats appear to have a strong chance of taking back the majority in the House, Republicans appear poised to hold on to the Senate.

Democrats need 23 seats to regain control in the Lower Chamber and FiveThirtyEight.com gives them a nearly 86 percent chance of taking the House. But the Senate map provides a difficult challenge.

Democrats are defending Senate seats in ten states that 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 won in 2016 and already needed to pick up two more seats to gain the majority in the Upper Chamber. FiveThirtyEight.com gives the Democrats only a 16 percent chance to win the Senate.

Some closer Senate races have shifted to the right in recent weeks.

A Quinnipiac University poll released on Monday showed Sen. Ted Cruz Rafael (Ted) Edward CruzSenate GOP set to vote on Trump's Supreme Court pick before election Supreme Court fight pushes Senate toward brink Crenshaw looms large as Democrats look to flip Texas House seat MORE (R-Texas) leading his opponent Rep. Beto O'Rourke Beto O'RourkeJimmy Carter says his son smoked pot with Willie Nelson on White House roof O'Rourke endorses Kennedy for Senate: 'A champion for the values we're most proud of' 2020 Democrats do convention Zoom call MORE by five points in their race, while Republican Josh Hawley has a slim lead over 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.) by an average of two points in Missouri's Senate race, according to Real Clear Politics.

RealClearPolitics average of polls also gives challenger Mike Braun (R) a slim edge in Indiana against Sen. Joe Donnelly Joseph (Joe) Simon DonnellyTrump taps Amy Coney Barrett for Supreme Court, setting up confirmation sprint Trump plans to pick Amy Coney Barrett to replace Ginsburg on court Harris faces pivotal moment with Supreme Court battle MORE (D).

— Julia Manchester