By Albert R. Hunt

Bloomberg View

All national elections are hyped as seminal. The midterms of 2018 are the real deal.

If Democrats win at least one branch of Congress, there will be an investigative feast — with rich targets — of the ethically challenged administration of President Donald Trump, plus a check on presidential actions. If Republicans retain full control, expect renewed attacks on Obamacare, efforts to cut Medicare and Social Security, and one or two more right-wing Supreme Court justices.

Equally significant will be gubernatorial and state legislative contests. These will serve either to complement or counter national policies, and will set the table for redistricting following the 2020 census.

The early line is good for Democrats. As the year commences, here’s how it looks:

House of Representatives

Most polls suggest that Democrats will gain the two dozen seats they’d need to take control. I’m even more taken by this assessment by Mark Gersh, who has tracked House races for Democrats for 40 years and is respected for prescience and caution. “Our chances are very solid,” he said in an interview last week. “The number 24 is not daunting.”

Democrats start with an advantage in contests for 14 Republican-held seats in the deep-blue states of California, New York and New Jersey. They expect to win most of those. They see promising opportunities in more than a dozen other states, multiple ones in a couple. In Iowa, for example, the reliable Iowa poll earlier this month showed Democrats running ahead of two Republican incumbents, one by a huge margin, and within striking distance of a third.

If a blue wave rolls through the electorate, Democrats could win even more, including supposedly safe Republican seats in states as diverse as Florida, Utah, Michigan and Virginia.

Republicans expect to lose seats, but think they’ll keep a narrow majority thanks to strong incumbents and lots of money. They also anticipate winning several seats held by Democrats in politically divided purple states like Minnesota.

Senate

The electoral map is daunting for Democrats when it comes to senators. They have to defend 26 seats, the Republicans only eight. To take over, Democrats need a net gain of two.

At the moment, six Democratic incumbents face difficult challenges, though two of them — Montana’s Jon Tester and West Virginia’s Joe Manchin — appear to be in good shape. Three Republican seats look competitive, and Democrats think at least one more will be in play either because a right-wing challenger supported by the Steve Bannon wing of the Republican Party will rough up a safe incumbent, or because of a surprise in Texas or some other demographically fluid state.

Even if all those factors break in the Democrats’ favor, they’d still be at a disadvantage. They’d have to win eight of the 10 competitive races — all but one (Nevada) in states carried by Trump last year. A must-win for Democrats is Tennessee, where former Governor Phil Bredesen will mount a strong challenge in a heavily Republican state. (Incumbent Senator Bob Corker is retiring.) Republicans would be concerned if they can’t unseat Senator Claire McCaskill in Republican-friendly Missouri.

Governors

There are 35 gubernatorial offices up for grabs, with 26 held by Republicans and one, in Alaska, by an independent. For Democrats, there’s a Big Five: Ohio, Florida, Michigan, Wisconsin and Pennsylvania. All but Pennsylvania are now in Republican hands.

What happens in these states can influence national politics. For one thing, they’re all battleground venues in presidential elections. But the biggest factor is the influence they will have on redistricting after the 2020 census.

In all five of these states, governors have veto power over any redrawn district map. After the 2010 census, Republicans reshaped congressional and state legislative districts through effective, partisan gerrymandering.

Statehouses

State legislatures are even more important than governors when it comes to redistricting. Republicans now enjoy overwhelming statehouse majorities in states where the 2016 presidential vote was close. Democrats will mount a major effort to cut into these margins with help from former President Barack Obama, who was asleep at the switch in the last redistricting fight, and are hoping to take over a couple of chambers. They will announce top targets in a few weeks.

Beyond the Big Five states, a fierce battle is brewing in North Carolina, where gerrymandering has given Republicans almost a 2-to-1 majority in the legislature and 10 of 13 U.S. House seats. In moves Vladimir Putin would admire, Tar Heel Republicans ruthlessly changed rules and procedures in 2016 after voters elected a Democratic governor, stripping him of many executive powers.

The nationwide outcome will be affected by legal rulings on challenges to the way many states draw legislative districts and a Supreme Court decision this session on gerrymandering cases from Wisconsin and Maryland. There are also efforts underway to set up ballot referendums in Michigan and, less likely, Ohio to create nonpartisan redistricting commissions.

Albert R. Hunt is a former executive editor of Bloomberg News, before which he was with the Wall Street Journal.