Brutal numbers show how tough it will be for Republicans to keep control of the House this November

Joshua Roberts/Reuters

President Donald Trump and House Speaker Paul Ryan

• This week's too-close-to-call special election in a ruby-red Ohio congressional district has called new attention to a 2018 electoral map that highly favors Democrats - at least in the US House.
• The minority party needs to flip 24 Republican-held seats this year to take control of the House.
• There are 68 GOP-held House seats that are less conservative than Ohio's conservative 12th district, where Tuesday's special election remains too close to call.

This week's too-close-to-call special election in a Republican-leaning Ohio congressional district has called new attention to a 2018 electoral map that highly favors Democrats - especially in the US House.

It looks unlikely that Democrat Danny O'Connor will successfully flip Ohio's 12th district (provisional ballots are still being counted). But the fact that a district President Donald Trump won by 11 points could so quickly turn against the GOP has many predicting a "blue wave" in this year's midterms.

And the numbers point in Democrats' favor:

• The minority party needs to flip 24 Republican-held House seats this year to take control of the 435-seat chamber.
• And Hillary Clinton won 25 districts that are current represented by Republicans.
• On top of that, there are 68 Republican-held House seats that are rated as less conservative than Ohio's 12th district, and 119 GOP seats less Republican than the seat Democrat Conor Lamp flipped in western Pennsylvania in March, according to an analysis from the non-partisan Cook Political Report.

Boosting Democrats' confidence are the president's relatively low approval ratings and stronger support for Democrats than Republicans in generic ballot polls.

But GOP strategist Matt Mackowiak cautioned that midterm turnout can be very different from presidential election year turnout - specifically, midterm electorates are typically less racially diverse.

"There's all this chatter about these so-called Hillary districts," he said. "Does that mean the Democrat could win? Yes. Does it mean the Democrat is guaranteed to win? No. ... Traditionally you've seen lower minority participation in midterm years."

But Mackowiak conceded that the map and political trends are alarming for Republicans.

"It's clear there's tremendous risk if you are in an R+10 district or worse," he said, adding that the "risks to the Trump administration if the Democrats take the House back are profound."

If Democrats win control of the legislative chamber, Republicans fear they'll use their subpoena power to aggressively investigate the president and his administration, kill the GOP's legislative agenda, and attempt to impeach him.

But the Senate is a different story. Of the 35 senators up for reelection this year, 26 are Democrats and just nine are Republicans. And 10 of these Democrats represent states Trump carried in 2016. On top of that, only two of the GOP-held seats on the ballot are in traditional swing states (Nevada and Arizona).

To flip the Senate, Democrats would need to win 28 of these races - a much more significant challenge than they have in the House.