Places to watch as Jon Ossoff and Karen Handel try to piece together a win on Tuesday.

Democrat Jon Ossoff and Republican Karen Handel face off Tuesday in a House special election that’s doubling as the biggest political test of Donald Trump’s presidency so far.

Ossoff and Handel got here by finishing first and second in an all-party primary on April 18 in Georgia’s 6th Congressional District in which Ossoff won 48 percent of the vote and Handel got 20 percent to advance to the runoff. But Republican candidates together had an edge in April, 51 percent to Democrats’ combined 49 percent.

That ultraclose result gives a useful lay of the land for Tuesday’s contest, which could be just as tight. The April results show the battlegrounds within the battleground district and where each party wants to run up the score on June 20.

What’s in play The district as a whole is closely divided, but not every neighborhood is. These maps show the precincts in which the combined Republican and Democratic vote shares were highest heights in the April primary, as well as where the margin between the parties was within just a few percentage points. Scroll over each precinct to see how the parties performed there in April. GOP Strongholds Republicans are strongest in Cobb County in the west of the district and the northern portion of Fulton County, where Handel got her start in elected office. Democrats’ safety net Democratic votes are concentrated in the southern tip of the district, in DeKalb County, as well as a strip of neighborhoods alongside U.S. Route 19, which bisects the district. Up for grabs Many of these evenly divided parts of the district used to lean Republican, but they swung to the left in the 2016 presidential race and the April special primary.

Opportunities Over 192,000 voters participated in April, and turnout is expected to rise even higher than midterm-election levels on Tuesday. Democrats and Republicans have spent two months hunting for voters who cast ballots in 2016 but didn’t participate in the April primary. The pool is bigger for Republicans than Democrats: About 59,000 Republicans and 31,000 Democrats who voted in the 2016 general election but stayed home in April, according to analysis by Optimus Consulting, a GOP analytics firm. There are also about 64,000 independents, who have leaned toward Ossoff in many polls but may be trickier to turn out to vote. Consider these maps. They show precincts in which the April margin between the losing party and the winning one was less than the number of votes the party is chasing from last November. Both parties’ best chance is to get the voters who cast ballots for president to the polls in June. The darker the precinct, the more votes are outstanding. Democrats’ opportunities GOP opportunities What’s already changed

Campaign Spending The special election has obliterated the previous all-time record for a House race, which was $29.6 million. The candidates and outside groups in Georgia have spent about $50 million.