In 2016, after all, Donald J. Trump won Michigan by just 10,700 votes — and the Libertarian candidate, Gary Johnson, won 172,000 votes in the state. Mr. Amash’s likely entry into the race, as a native son in a state that is again likely to be a battleground, gave some Democrats and Never Trump Republicans overnight heart palpitations.

Nonetheless, strategists from both major parties in Michigan said on Wednesday that this year’s electoral landscape was so fundamentally altered from four years ago that Mr. Amash was not likely to have a major impact in the state, or on the general election as a whole. If Mr. Trump’s surprising victories in Northern industrial states in 2016 were based on high levels of dislike for the Democratic nominee, Hillary Clinton, which depressed Democratic turnout, those appear to be lesser factors this time around as he prepares to face Joseph R. Biden Jr…

McNeilly, who lives in Mr. Amash’s House district in Western Michigan, said the deciding factor this year would be how large a share of its base each party is able to turn out — and that formulation favors Mr. Biden, a more popular candidate with Democrats than Mrs. Clinton was when she lost the state by just 0.3 percentage points.

“Trump didn’t win Michigan in 2016; she lost it,” Mr. McNeilly said, referring to Mrs. Clinton, the first Democratic presidential candidate to lose the state in a generation.