The Republicans’ battle to win back control of Congress kicks into high gear Tuesday, as Ohio and Indiana hold primaries. 

The GOP needs a net gain of five seats in the House and one in the Senate to take full control of Capitol Hill next year. 

And history is on the Republicans’ side. 

The party in the White House traditionally loses seats in the first midterm after a new president takes office. Meanwhile, President Joe Biden’s poll numbers are underwater — a recent ABC News-Washington Post poll found that 42% approve of the job he’s doing, while 52% disapprove. While that poll showed improving numbers for the president's job performance and also showed Republicans losing their 10-point lead in the generic Congressional ballot, Democrats still face headwinds heading into November. 

Texas is the only other state to have held primaries so far this year, but races will be hold nearly every week from now into September.

Here’s a look at some of Tuesday’s key primaries:

Ohio Senate

Seven hopefuls are vying for the GOP nomination to succeed the retiring Rob Portman, also a Republican. It has been a hotly contested race, with candidates and interest groups spending a state record $66 million on advertising. 

Last month, Donald Trump endorsed J.D. Vance, giving a boost to the “Hillbilly Elegy” author and onetime never-Trumper. Vance has since apologized and said he was wrong for being critical of Trump, which included calling him “an idiot.”

Most of the Republicans Vance is facing have been firmly in Trump’s corner, namely former state Treasurer Josh Mandel, who has been running on the slogan, “Pro-God, pro-gun, pro-Trump.”

Strangely enough, Trump confused the two competitors this past weekend, telling the crowd at a rally in Greenwood, Nebraska, that he endorsed “J.D. Mandel.”

State Sen. Matt Dolan, whose family owns the Cleveland Guardians baseball team, is the only Republican candidate putting distance between his campaign and Trump, although he says he still supports the former president.

The race is being closely watched nationally to determine if Trump still maintains substantial sway over the party.

Recent polls have Vance leading by 2 to 5 percentage points, with Mandel and Dolan in striking distance. 

Other candidates are Cleveland investment banker Mike Gibbons, former Ohio Republican Chair Jane Timken, and entrepreneurs Mark Pukita and Neil Patel. Portman has endorsed Timken. 

In the general election, the GOP primary winner will face one of three Democrats: 10-term U.S. Rep. Tim Ryan, former consumer protection attorney Morgan Harper, and activist and tech executive Traci Johnson.

Ryan leads big in the polls.

Indiana Senate

The Senate primaries in Indiana are merely a formality, as the Republican and Democratic candidates are running unopposed. 

In February, the bipartisan Indiana Election Commission voted to uphold challenges to the eligibility of three other candidates who fell short of signature requirements. 

Republican Todd Young is seeking a second term. Before being elected to the Senate in 2016, he served four terms in the House. 

Young will face Hammond Mayor Tom McDermott Jr. in the general election. 

Young has outraised McDermott 4-to-1 in a race the Cook Political Report rates as solidly Republican.

3 ‘toss-up’ Ohio House races

Of the 26 House races nationally that the Cook Political Report rates as “toss-ups,” three are in Ohio.

The primaries are being held despite ongoing legal challenges to Ohio’s congressional districts, as well as its state legislative districts. 

For that reason, state races are being put on hold, but congressional races are moving forward using a map that has been invalidated by the Ohio Supreme Court. A new map could be in place before 2024.

In the 9th District, Marcy Kaptur, the longest-serving woman in Congress, is running unopposed for the Democratic nomination. She, however, will face perhaps her biggest challenge in the general election since first being elected 40 years ago, as outside groups have spent a combined $1 million on the race.

Four Republicans are running to unseat Kaptur: veteran services program manager Beth Deck; state Sen. Theresa Gavarone; Air Force veteran J.R. Majewski, who now works in the nuclear energy industry; and state Rep. Craig Reidell.

The district stretches from Cleveland to Toledo along Lake Erie. 

In Ohio’s 1st District, Republican six-term incumbent Steve Chabot faces a challenge from Christian activist Jenn Giroux. On the Democratic side, Cincinnati City Councilman Greg Landsman, a former teacher, is running unopposed.

The district, which includes much of Cincinnati, has been represented by a Republican for all but two years since 1995.

Seven Republicans are running to replace Ryan in the newly redrawn 13th district: attorney and former beauty queen Madison Gesiotto Gilbert; Shay Hawkins, a former aide to Sen. Tim Scott and ex-Rep. Jim Renacci; foreign policy journalist Santana King; anti-abortion activist Janet Folger Porter; communications consultant Dante Sabatucci; construction project engineer Ryan Saylor; and attorney and accountant Greg Wheeler.

The winner will face Democratic state Rep. Emilia Sykes, who is unopposed in the primary.  

The district, which is located in the northwest part of the state and includes Akron, has not been represented by a Republican since Charles Adams Mosher retired in 1977.

Indiana’s 1st Congressional District

No Republican has represented Indiana’s 1st Congressional District since the Great Depression, but sensing it might be ripe to flip, seven candidates are running for the GOP nomination this year.

Adding to the intrigue, Cook Political Report and Sabato’s Crystal Ball have changed their ratings for the district from likely Democratic to leaning Democratic, nudging it closer to toss-up territory. 

The district in the northwest corner of the state just outside Chicago is currently represented by freshman Rep. Frank Mrvan, who is expected to coast to victory in the primary against challenger Richard Fantin, who hasn't raised enough money to be required to file a campaign finance report. 

The two leading Republican candidates are Blair Milo — a Navy veteran, former La Porte mayor and former aide to ex-Gov. Eric Holcomb — and Jennifer Ruth-Green —  an Air National Guard veteran and political newcomer.