Tuesday is the deadline to register to vote in Oregon’s May 17 primary. Here’s what you need to know:

1. Oregon generally has voting rules aimed at maximizing participation, but not when it comes voter registration.

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Eleven states allow voters to register as late as election day. Oregon also once did. But that changed after a cult headed by Bhagwan Shree Rajneesh set up a commune in rural Wasco County.

Among other things, the group tried to take over county government by busing in homeless people who they would register to vote. State officials blocked the Rajneeshees from doing that, but the uproar led to a 1986 ballot initiative that cut voter registration off 21 days before the election.

2. The early deadline could be particularly important for this primary.

That’s because it’s also the deadline for changing your party registration – and this really matters now.

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There are still live nomination battles in both the Democratic and Republican parties. That’s unusual because Oregon votes so late in the primary season (only seven states have a later primary or caucus).

However, Oregon Democrats and Republicans both hold closed presidential primaries, meaning that only party registrants can participate. If you want to #FeelTheBern or tell Hillary Clinton #ImWithHer, you have to be a Democrat. And you have to be a Republican if you want to weigh in on Donald Trump, Ted Cruz or John Kasich.

3. Oregon is starting to automatically register voters using DMV data – but there are still a lot of people eligible to vote who aren't registered.

As the result of a 2015 law, Oregon’s election officials are beginning to register people using data from the Driver & Motor Vehicle Services Division.

Eventually, this could add hundreds of thousands of people to the voting rolls. But not yet. The Secretary of State’s Office has estimated there are around 3 million adult citizens in Oregon who meet the criteria for voting. As of the end of March, only about 2.24 million are actually registered.

4. Here are three easy ways to register to vote.

Register online at the Secretary of State's office no later than 11:59 p.m. Tuesday. If you're unsure of your registration status, you can also check it at the same site.

Obtain a voter registration card at many public offices, fill it out and mail it back. It has to be postmarked no later than Tuesday.

Go to a county elections office and register there, but you have to do it before the close of business.