David Shribman is the former executive editor of the Pittsburgh Post Gazette.

SAGINAW, Mich. — Move over, Pennsylvania. This is a keystone state, too.

Pennsylvania lays its claim for Keystone State status for purely geographical reasons. Sitting there virtually in the middle of the 13 Colonies, Pennsylvania earned its name because it, like the keystone in an arch, held the whole structure together as the United States itself came together in the mid-1770s.

But historically, Michigan has been a keystone state as well and has just as realistic a claim to the title. It was at the center of the iron, copper and timber trades that led America into its industrial transformation. Its position on the Great Lakes transport corridor made it a cog in the great movement of resources across the continent. For decades, its motor-car industry was the engine of the country’s economy.

Then there is the political profile of Michigan. In Pennsylvania’s more than 2 1/3 centuries of its political existence, all its lawmakers combined haven’t had the impact of a single Michigan lawmaker, Sen. Arthur Vandenberg. When the Republican from Grand Rapids delivered his landmark 1945 speech announcing his conversion from isolationism to internationalism, the country swung decisively with him. That debate was over — until Donald Trump rekindled it.

Plus this: When Michigan’s economy slumped in the 1970s, the United States slumped with it.

So there is a certain poetry — a word seldom associated with either state, Edgar A. Guest excepted — to the fact that Michigan, for the duration of this column anyway, has joined Pennsylvania as a keystone state — or, as political professionals call them, swing states. It isn’t too much to say that the 2024 election could be determined in the two states.

Michigan, which joined the Union 61 years after the Declaration of Independence, voted Republican for the four elections beginning in 1972 and then Democratic for the six beginning in 1992. Trump eked out a slender victory in 2016, but Joe Biden captured it four years later. A swing state, indeed.

“Michigan has been a toss-up state for many years, and Democrats need to work hard to win here,” former Democratic Gov. James Blanchard said the other day as he was preparing to dip into a Detroit television station to speak for the Biden campaign. “We’ll be seeing these candidates once a week.”

Now, just as Pennsylvania has a luminous Democratic governor (Josh Shapiro, a sure topflight presidential candidate in 2028), Michigan has one as well, with four more years of gubernatorial experience (Gretchen Whitmer). Not a few analysts, including this one, have wondered whether a Whitmer-Shapiro ticket this November would win 40 states for the Democrats — but that’s a question for another day, though perhaps sooner than anyone might have expected.

Biden has opened 15 field offices here. Trump was here last month, speaking at a Black church. The two will crisscross the state several times before Election Day, and it would surprise no one to find them in Michigan on the same day — or days. It’s that critical. Democrats are slightly more confident of their prospects in Pennsylvania than in Michigan, so Biden may be the more frequent visitor.

Right now, Trump holds a 2.4 percentage-point advantage over Biden here, according to the 538 polling average. That is basically nothing; a fluttering of a butterfly in Fordlandia, Brazil — the prefab industrial community that Michigan’s Henry Ford established in the Amazon rainforest 96 years ago — would be enough for the two major-party candidates to swap places atop the slate, especially since Independent candidate Robert F. Kennedy Jr. clocks in at 8.7% of the vote here. That’s why both candidates fear, if not respect, the son of the late New York senator.

More than Pennsylvania, Michigan is a microcosm of contemporary American politics.

Blanchard, the first Democratic governor in 20 years and a four-term member of the House of Representatives who was preceded and succeeded by Republican lawmakers, explained that commentators often oversimplify Michigan’s political profile. “It’s not just one group, but every group that’s important in this state, and especially in this election,” he said. “Yes, Michigan is a labor state, and it’s a Black state, and an Arab state, and it has a large Jewish community. Don’t rule out the suburbs as important here. They will be the key, along with the west side of the state, which seems to be trending toward Democrats. But we have to put in the work.”

The Democrats are divided between progressives and moderates, a chasm widened by the disaffection of Arab Americans over Biden’s policies in the Israel-Hamas war. In the spring Democratic presidential primary, he faced a rebellion in the cities of Dearborn, Dearborn Heights and Hamtramck, all with heavily Arab American populations. Indeed, the 100,000 Democratic primary voters who cast ballots for “uncommitted” — an action urged by Rep. Rashida Tlaib, who represents Dearborn and is the first Palestinian American woman to serve in Congress — tarnished Biden’s victory here.

Not that the Republicans are unified. While the Gerald Ford style of Republicanism — quiet and respectable rather than noisy and rebellious, a formula that worked for him for the quarter-century from 1949 until 1973, when he became vice president — is in eclipse, Michigan’s Republicans haven’t fully embraced the Trump insurgency. The state GOP is a mess, reflecting conflicting views of Trump and his MAGA movement. A long struggle to remove state chair Kristina Karamo, a Trump ally, from office finally succeeded; Pete Hoekstra, who served in Congress and was a Trump-appointed ambassador to the Netherlands, emerged as new chair and has begun to right the ship.

“The Republicans were getting killed, so that will help Trump in November,” said Bill Ballenger, a former Republican member of the state House and Senate before becoming a top political analyst in Michigan. “But it remains a very tight race here. It is going to go back and forth every day from now until the day of the election.”

The distance between Tlaib and Karamo — from the far left to the far right — speaks volumes about how contemporary America is divided politically. It also speaks to the changes in political life in this swing state, which within living memory had important governors from the mainstream of the Democratic Party, like G. Mennen Williams (1949-1961) and Blanchard (1983-1991), and from the mainstream of the Republican Party, like George Romney (1963-1969) and William Milliken (1969-1983). Could any of them be elected today?