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WASHINGTON (AP) — Oregon's Democratic Gov. Tina Kotek and the nearly two dozen challengers hoping to defeat her are among the candidates who will seek their parties' nominations for state and federal offices in Tuesday's primary. Voters will also decide a statewide ballot measure that would raise gas taxes to pay for improvements to the state's roads and bridges.

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National politics cast a long shadow over the primary, as is often the case in a midterm election year, when voters historically have punished the incumbent president's party at the ballot box. Kotek has made President Donald Trump a top foil in her campaign, while the vote on Measure 120 to raise vehicle fees and gas taxes for transportation infrastructure projects takes place against the backdrop of gas prices that have steadily climbed since the start of the Iran war.

Kotek faces nine Democratic primary challengers in her bid for a second term. The Republican primary field features 14 candidates, including Marion County Commissioner Danielle Bethell, state Rep. Ed Diehl, state Sen. Christine Drazan and financial planner and former NBA player Chris Dudley. Dudley last ran for governor in 2010, when he received about 48% of the vote in the general election.

Incumbents are also running for reelection for U.S. Senate and all six U.S. House seats, with only one member of Congress facing no opposition for renomination.

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The key counties in both Democratic and Republican primaries are Multnomah, Washington and Clackamas counties in the Portland area and Lane County, which is home to Eugene. Salem-based Marion County, Jackson County and Deschutes County also contribute significant amounts of vote in both parties' primaries.

Dudley won the 2010 primary for governor with 39% of the vote against eight candidates. Of the most populous counties, he carried Multnomah, Washington, Clackamas and Washington counties and placed second in Lane County.

Here are some of the key facts about the election and data points the AP Decision Team will monitor as the votes are tallied.

When do polls close?

Oregon elections are conducted predominantly by mail. Ballots delivered to a ballot drop box or a county elections office must be received by 8 p.m. local time, which is 10 p.m. ET and 11 p.m. ET. Counties have the option to keep their locations open longer. Almost all of the state observes Pacific time, so the deadline in those areas is 11 p.m. ET. Some of the state observes Mountain time and the deadline there is 10 p.m. ET. Mailed ballots must be postmarked by 8 p.m. local time and received by May 26 to be counted.

What's on the ballot?

The AP will provide vote results and declare winners in contested primaries for U.S. Senate, U.S. House, governor, state Senate and state House, as well as for Measure 120 and the nonpartisan race for state labor commissioner.

Who gets to vote?

Voters must be registered with a political party to participate in that party's primary. Democrats may not vote in the Republican primary or vice versa. Independent or unaffiliated voters may not participate in either primary.

How many voters are there?

As of May 4, there were about 3.1 million registered voters in Oregon, including about 988,000 registered Democrats and about 737,000 registered Republicans.

How many people actually vote?

Registered Democrats cast between 420,000 and 456,000 votes in the 2024 primaries, depending on the contest, while registered Republicans cast just shy of 300,000 votes.

Turnout was higher in the 2022 midterm primaries, when Democrats cast between 478,000 and 492,000 votes and Republicans cast between 347,000 and 370,000 votes.

How much of the vote is cast early or by absentee ballot?

Oregon has conducted vote-by-mail elections since the 1990s. Ballots may also be delivered to drop boxes and county elections offices.

As of Friday, nearly 513,000 ballots had already been cast in Tuesday's election.

When are early and absentee votes released?

Since Oregon elections are conducted predominantly by mail, results from mail voting are released throughout the night and the following days. A handful of smaller counties release all or most of their results from Election Day voting in their first vote report.

How long does vote-counting usually take?

In the 2024 presidential and state primary, the AP first reported results at 11 p.m. ET just as the final polls closed. The last vote update of the night was at 5:11 a.m. ET with about 74% of total votes counted.

When will the AP declare a winner?

The Associated Press does not make projections and will declare a winner only when it's determined there is no scenario that would allow a trailing candidate to close the gap. If a race has not been called, the AP will continue to cover any newsworthy developments, such as candidate concessions or declarations of victory. In doing so, the AP will make clear that it has not yet declared a winner and explain why.

How do recounts work?

Recounts in Oregon are automatic in the event of a tie vote or if the vote margin is 0.2% of the total vote or less. The AP may declare a winner in a race that is subject to a recount if it can determine the lead is too large for a recount or legal challenge to change the outcome.

Are we there yet?

As of Tuesday, there will be 168 days until the 2026 midterm elections.

-- Robert Yoon, Associated Press