Tuesday’s special election to fill a vacant Alabama Senate seat seems close enough to provide real drama.

Polls show the race narrowed last month after Republican nominee Roy Moore was repeatedly accused of sexual misconduct with teenagers, which he has denied. Even before that, Mr. Moore’s strength in a statewide race was in doubt. In 2012, when Republican Mitt Romney drew 61% in the presidential race in Alabama, Mr. Moore drew a smaller 52% share in his successful race for chief justice of the state’s Supreme Court. Mr....

Tuesday’s special election to fill a vacant Alabama Senate seat seems close enough to provide real drama.

Polls show the race narrowed last month after Republican nominee Roy Moore was repeatedly accused of sexual misconduct with teenagers, which he has denied. Even before that, Mr. Moore’s strength in a statewide race was in doubt. In 2012, when Republican Mitt Romney drew 61% in the presidential race in Alabama, Mr. Moore drew a smaller 52% share in his successful race for chief justice of the state’s Supreme Court. Mr. Moore’s opponent, Doug Jones, if successful, would be the first Alabama Democrat elected to the U.S. Senate in 25 years.

As the votes roll in, here are some key places and constituencies to watch for:

The GOP has a number of options when it comes to dealing with Alabama senate candidate Roy Moore, who has been mired in sexual misconduct allegations, but each one presents a dilemma for the party. WSJ's Shelby Holliday explains. Photo: Getty Images.

The Romney/Not-Moore Counties: In 2012, nine counties in Alabama voted for Mr. Romney for president while rejecting Mr. Moore for the state Supreme Court on the same ballot. They were Butler, Chambers, Choctaw, Clarke, Madison, Mobile, Pickens Pike and Tuscaloosa.

Some of those counties have large African-American populations (Choctaw and Clarke), while others have large populations of young voters (Tuscaloosa)—two groups that have the potential to help Democrats balance the Republican tilt of the electorate. If Mr. Moore struggles in those counties again on Tuesday, that’s a bad sign for him. If he wins a few of them, he can relax a bit.

Advertisement

Upscale, Establishment Republicans: The civil war playing out within the GOP nationwide is alive in Alabama, as well. In the September primary, Mr. Moore defeated sitting Republican Sen. Luther Strange, but Mr. Strange won four counties in the state. They included Jefferson, Madison and Shelby.

Those counties are all above the state averages for income and share of residents with a four-year college education, characteristics that align with a centrist brand of Republicanism.

Keep an eye on Madison County, home of Huntsville. It’s the kind of place where the Trump wing of the GOP is more muted, and the county may give a sign of how close the race will be.

Mr. Romney won 58% of Madison’s vote in 2012, while Mr. Moore won 48%. In 2016, Mr. Trump drew seven percentage points less in the county than he did statewide.

Advertisement

If Mr. Moore underperforms his 48% of the 2012 election, that’s a sign of trouble for him.

Mr. Moore’s Base: In the northwest corner of Alabama is a cluster of counties that gave Mr. Trump at least 73% of the vote. They include Franklin, Lawrence, Winston and Marion.

In those counties, African-Americans account for less than 12% of residents, and relatively few people have bachelor’s degrees. The voter profile in these counties is a good match for Mr. Moore’s message.

This corner of the state is also populated relatively sparsely and holds a large number of evangelical adherents. Mr. Moore is sure to run up big margins here, but he will need turnout to be strong—at nearly presidential levels. If total votes cast are 9,000 to 10,000 in Franklin and Winston and 10,000 in 12,000 for Lawrence and Marion that will be a sign of enthusiasm among Mr. Moore’s base voters.

Advertisement

African-American Turnout: Ten counties in the southern half of the state vote reliably Democratic in presidential races—Bullock, Dallas, Greene, Hale, Lowndes, Macon, Montgomery, Perry, Sumter and Wilcox. They have backed the Democrat in every presidential election since 2000, and all of them gave Hillary Clinton 59% or more of their vote in 2016. In all of them, African-Americans account for half or more of the population. Statewide, about 28% of voters are African-American, census data show.

Mr. Jones needs to win these counties comfortably, but he also will want something close to presidential turnout from them. Especially crucial is populous Montgomery County, in the south-central part of the state. If it produces something close to the 95,000 votes it did in the presidential election last November, that’s a good sign for Mr. Jones.

Write to Dante Chinni at Dante.Chinni@wsj.com