Candidates for D.C. mayor made final preparations Monday to get core supporters to the polls for the Democratic primary, an effort that could make all the difference in an election widely expect to attract low participation.

Polls opened to clear skies at 7 a.m. Tuesday after two weeks of weather-dampened early voting in an election that has generated little excitement across the city. The front-runners — incumbent Vincent C. Gray (D) and D.C. Council member Muriel Bowser (D-Ward 4) — agreed that the outcome would hinge on turnout.

In every modern mayoral election in the heavily Democratic District, the winner of the primary has gone on to be mayor.

After leading by double digits in polls early in the year, Gray’s ability to keep voters focused on his stewardship of the city’s growing economy was shaken in early March when a major campaign donor pleaded guilty to illicit spending on behalf of Gray’s first mayoral bid four years ago.

From a field of seven challengers that includes three other council members, Bowser emerged as Gray’s main competitor. In a recent Washington Post poll, the two were locked in a statistical dead heat.

In Gray’s Northeast Washington campaign headquarters the day before the election, the driving beat of James Brown’s “Don’t Tell It” blared as staff members numbered 143 hulking blue Ikea bags — one for each city polling precinct — and stuffed them with campaign signs, clipboards and forms to count voters.

Shaking hands in the parking lot of a windswept Giant grocery store on Rhode Island Avenue in Brentwood, Gray said he was confident that his record made him the better-prepared candidate.

“I’m very encouraged by where we are. . . . We’ve been working very hard on those who supported us four years ago and we feel very hopeful and expectant that they will turn out,” he said.

Gray turned to reporters and laughed when asked if he thought he could win. “Win? ‘W-I-N,’ that is our strategy. . . . We have a record that is very sound. . . . Look at unemployment: down.”

At Bowser’s headquarters, boxes filled weeks ago with the same supplies Gray’s workers were preparing for the precincts were pulled from a closet, along with pallets of water bottles to hand out on Election Day.

Left hidden at both offices were the coveted lists of surefire supporters compiled over months of repeated phone calls and home visits. Bowser’s senior campaign aides planned to distribute many of those to volunteers at a pre-dawn rally Tuesday to launch the final push to get out the vote with door-knocking and phone calls.

Bowser began the last day of campaigning early in the morning surrounded by sign-waving supporters at Georgia and Missouri avenues NW. “I need your vote,” she told many rush-hour commuters, approaching them with an outstretched hand.

According to polls, council member Tommy Wells (D-Ward 6) was the closest remaining of six other candidates on the ballot, ahead of council member Jack Evans (D-Ward 2), council member Vincent B. Orange (D-At Large), restaurateur Andy Shallal, former State Department official Reta Jo Lewis and musician Carlos Allen.

Bowser’s last public event came early Monday, at lunchtime, with a visit to the 100th anniversary gathering of the Washington Animal Rescue League. Aides said she was in meetings and with family later in the day.

She had been focused on Tuesday, aides said, when she began the day with the 5:30 a.m. rally.

But Bowser’s tweets continued late into the evening, with some directed at the ongoing investigation of Gray’s first campaign: “If you believe our mayor must have INTEGRITY, then vote Muriel tomorrow.”

In an almost mirror image, Gray began Monday by greeting commuters while surrounded by 20 supporters clad in his royal-blue campaign T-shirts at the Benning Road Metro stop in Northeast. He then returned to city government headquarters and didn’t resume his campaign schedule until mid-afternoon, missing a planned lunchtime stop at the Rhode Island Row development.

Aides said he attended a long-scheduled meeting with City Administrator Allen Lew to put final touches on his annual budget presentation to the council, set for Thursday morning.

Hours later, word leaked that the mayor had also signed a bill Monday to decriminalizing small amounts of marijuana, replacing criminal penalties with a civil fine of $25 for possession of less than an ounce of the drug.

Every mayoral candidate has touted the measure as a social-justice issue since a study last year found that nine in 10 arrested for simple drug possession in the District are African American. The measure has been popular citywide, but especially in Ward 7 and Ward 8 east of the Anacostia River, predominantly black areas where Gray will need a robust turnout to repeat his victory from four years ago. Wells, who authored the bill, issued a statement titled “DC Signs Marijuana Decriminalization Bill Championed by Wells,” downplaying the mayor’s role.

None of the final-day maneuvering altered the fact that the city would enter Tuesday with the outcome of the primary less certain than at any point in a quarter-century.  Not since 1990 have two leading candidates been so close heading into a mayoral election.

This time, a precipitous drop in early voting numbers and an earlier than normal primary have left some predicting the first drop in primary bollot tally in two decades.

Gray’s campaign manager, Chuck Thies, said moving the mayoral primary from September to April for the first time would likely mean turnout of no more than 100,000 people. The earlier date was set to comply with federal law meant to accommodate overseas voters.

The last drop in turnout followed a surge in 1994 to return Marion Barry to power. The former mayor and current Ward 8 council member has campaigned vigorously in the past week for Gray.

“My coattails are the longest,” Barry said Monday, predicting a victory for Gray and promising to visit every polling place in Ward 8 on Tuesday.

Tuesday promised to be full of candidate theatrics, with Gray planning to appear in Bowser’s home ward and Bowser promising to crisscross the city repeatedly.

One advantage for them — and voters — was that for one of the first times in months, the temperature was forecast to be in the 60s and mild.