DETROIT – Michigan and Ohio might seem to have a lot in common, and in some ways they do. Both have economies that have large and troubled manufacturing sectors, plus significant agriculture.

          They are roughly similar in size, and depend heavily on the Great Lakes and the St. Lawrence Seaway. But when it comes to politics, they are entirely different creatures.

Two years ago, the national Democratic “wave” was barely a ripple in Ohio, where the party failed to capture an open seat for governor and only reaped a handful of seats in the lower house of the Ohio General Assembly.

But it was a tidal wave in Michigan. Democrats won all the statewide offices, captured two formerly Republican congressional districts, and made big gains in both houses of the legislature.

The states differ in another way, too. Ohio holds its primary election for all offices together with its presidential primary.

Michigan has two primaries – the presidential in March, and the primary for everything from state representative to the U.S. Senate in early August – this year, on August 4. That is an important election this year for a number of reasons. Since most legislative seats have been gerrymandered to be safe for one party or the other, the August election is essentially the real election.

That’s true for some Congressional seats as well. Michigan’s 10th District, which includes most of the state’s “thumb” is an open seat this year; the incumbent, U.S. Rep. Paul Mitchell, is retiring.

But nobody thinks the Democrats have any chance here, and the winner of the Republican primary is virtually certain to be the next member of Congress.

A mirror-image of that is true in Michigan’s 13th District, now held by one of the nation’s most famous news members of Congress, “squad” member Rashida Tlaib.  A year ago, she was thought to be vulnerable in this year’s primary. She is a Muslim of Palestinian descent, and the district is overwhelmingly African-American.

She won nomination two years ago with 31 percent, mainly because a number of prominent black candidates split the vote. This year, she has only one primary challenger, Detroit City Council President Brenda Jones, who finished second in the last race.

But since then, Ms. Tlaib has become nationally famous, while still managing to be a major presence in the district.  She has also raised vastly more campaign funds than her challenger.

She’s become the favorite … but Michigan voters have been known to surprise the experts in primary contests.  Whoever wins the primary here, by the way, will have little trouble in November; last time, the GOP didn’t even have a candidate on the ballot.

There’s another interesting race in the Grand Rapids area, for a seat in Congress once held by President Gerald Ford and which is now held by U.S. Rep. Justin Amash.  Amash is running for reelection – but as a Libertarian, not a Republican.

Republicans have a crowded primary, with the favorite being Peter Meijer, a 32-year-old scion of the Michigan grocery chain. Normally, he would be a heavy favorite in the fall. 

But the district has been trending more Democratic, and some see a chance that if Amash manages to split the conservative vote Democrat Hillary Scholten just might win.

Monroe County, on the Ohio border, is also worth keeping an eye on. Once usually Democratic, it switched over to strongly support Donald Trump four years ago.  Its two state legislative seats have also switched from Democratic to Republican during the past decade.

They will be worth watching this year, however. Four years ago,  Republican Joe Bellino upset incumbent Democrat Bill LaVoy, the only seat the GOP gained that year.

Two years ago, LaVoy’s wife, Michelle LaVoy, tried and was also defeated by Bellino.  This year, with neither LaVoy running, the incumbent is trying for a third and final term.

There’s no incumbent in Monroe County’s other district, where State Rep. Jason Sheppard is retiring; while the district leans Republican, it elected a Democrat as recently as 2008.

That’s a date, by the way, that should shed shudders down some Republican spines.  That was the year that Republican Presidential nominee John McCain decided in October that Michigan was unwinnable, and pulled his campaign out of the state.

Barack Obama then won by 16 points, and Democrats won a thumping 67-43 majority in the state House of Representatives. Now, Michigan Republicans are uneasy about a repeat performance. President Trump, who barely won Michigan last time, trails Democratic candidate Joe Biden by 16 points in the latest EPIC-MRA poll  (55 to 39 percent) and by anywhere from nine to 14 points in other surveys.  A loss of that magnitude might mean disaster.

Not only might Democrats take control of the state house, two or three more congressional seats may be endangered. The upcoming primary won’t settle that — but both sides are hoping to nominate the strongest candidates possible ahead of November.

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Campaign footnote: One other thing to watch for:  How many people vote by mail — and how well Michigan deals with an avalanche of mail ballots.

 Secretary of State Jocelyn Benson sent every voter in the state an application for an absentee ballot for both August and November because of the coronavirus pandemic.  This worked well in local Michigan elections in May, when 99 percent voted by mails.

But the turnout then was tiny – and in last month’s U.S. Senate primary in Kentucky, it took a week to count enough votes to declare a winner.  (Editor’s Note: A version of this column also appeared in the Toledo Blade.