Voters are electing two governors, a few big-city mayors, one member of Congress and deciding a first-in-the-nation ballot measure in an election dominated by local and state races.

Here is a rundown of the top races on Tuesday's ballot:

TWO GOVERNORS

Voters in two states are choosing replacements for their term-limited governors — Democrat Terry McAuliffe in Virginia and Republican Chris Christie in New Jersey — in contests seen as an early referendum on the presidency of Donald Trump. In swing-state Virginia, most polls show a close race between Republican Ed Gillespie and Democratic Lt. Gov. Ralph Northam. In New Jersey, Democrat Phil Murphy holds a double-digit lead in the polls over Republican Lt. Gov. Kim Guadagno.

The stakes are high as both parties seek momentum ahead of next year's mid-term elections. Democrats haven't won any special elections for Congress this year and the next Virginia governor will have a major say in the state's next round of redistricting, when Congressional lines are drawn. Republicans are looking for a boost as their party is beset by intraparty turmoil between Trump and key Republicans in Congress.

BIG-CITY MAYORS

New York City Mayor Bill de Blasio holds a commanding lead in the polls as voters decide whether he deserves a second term. De Blasio, a Democrat, made political missteps in his first term but is expected to easily defeat a young, Republican challenger from Staten Island, Nicole Malliotakis, and the private detective and TV commentator, Bo Dietl.

In Boston, Mayor Marty Walsh asks voters to give him a second four-year term. Challenger Tito Jackson, a member of the City Council who would be the city's first black mayor, has been making the case for change.

MEDICAID

Maine residents vote in the nation's first statewide referendum on whether to expand Medicaid under the Affordable Care Act, a vote viewed as a referendum on "Obamacare." Thirty-one other states have joined the expansion, but this is the first time it has been put before voters. The ballot measure comes after Maine's Republican governor vetoed five attempts to expand the program.

UTAH'S CONGRESSIONAL SEAT

Utah voters are choosing a replacement for U.S. Rep. Jason Chaffetz after the Republican's surprise resignation earlier this year. John Curtis, the Republican mayor of the Mormon stronghold of Provo, is expected to sail to victory in a congressional district where Republicans outnumber Democrats 5-to-1. He is challenged by Democrat Kathryn Allen and third-party candidate Jim Bennett.

PHILADELPHIA DISTRICT ATTORNEY

Voters in Philadelphia are picking a new district attorney to replace Seth Williams, who was sentenced to prison last month for accepting a bribe. Larry Krasner, a liberal Democrat who vows to end mass incarceration and the death penalty, is favored to win in the heavily Democratic city. His opponent, Republican Beth Grossman, has gotten a boost with endorsements from The Philadelphia Inquirer and the local police union.

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