NORRIDGEWOCK, Maine — Could towns like this, a tiny crossroads of fewer than 1,300 households — now draped in brilliant autumn foliage colors, by Election Day perhaps resting quietly under a gentle dusting of snow — decide whether Democrats or Republicans rule the House? Or whether subpoena-assisted investigations are mounted against President Donald J. Trump and Supreme Court Justice Brett Kavanaugh?

Could Republican Rep. Bruce Poliquin be defeated by challenger Jared Golden, who left college shortly after the 2001 terrorist attacks to join the Marines and who is campaigning with the new moderate Democratic rhetoric full of the words “change” and “service” and “leadership”?

These are some of the mysteries of the 2018 midterm elections, which will deliver an important national message — who’s in control of the House, who runs the Senate — but will be determined in 370 separate elections. None are quite as distinctive as the one being conducted in this Maine congressional district, which delivered a single electoral vote for Trump two years ago; which has many of the distinctive markings of Trump territory; which has been targeted by the Democratic Congressional Campaign Committee as a potential party pick-up; and which is regarded as evenly split between the two parties and candidates.

“Races like this in Maine,” former GOP Sen. Olympia Snowe said in an interview, “often come down to the small towns.”

Maine is an idiosyncratic state by any measure: It has jagged mountains in the west and a rocky seacoast in the east. It is a complex combination, a tourist retreat for the wealthy and the home of many rural poor voters. Its politics have peculiarities that come only with a state that has had governors and now a senator who are Independents — in party name and in inclination. It awards single electoral votes for president from each of its two congressional districts.

The Poliquin-Golden congressional race will be determined by ranked choice voting,…