For the first time in decades, there will be real competition in this year's California presidential primary, which will be a crucial must-win state for Donald Trump to win the Republican nomination.

However, there is plenty of other excitement going on in the state, from a hotly contested Senate race to a statewide ballot initiative on disciplining state legislators. Read on to learn who will be on the ballot, what issues will be addressed, and how to vote.

The Presidential Primary

After sweeping five states this week, Donald Trump may have a path to winning the Republican nomination outright and avoiding a contested convention. But that depends on whether he can win in California.

According to a recent USC Dornsife/Los Angeles Times poll, Trump is currently leading in California.

On the Democratic side, the nomination contest is virtually resolved: according to the Los Angeles Times, Hillary Clinton has already amassed around 90 percent of the delegates needed to win the nomination. However, Bernie Sanders plans to remain in the race through the California primary to attempt to gain influence to liberalize the Democratic party platform.

In California, some parties hold closed primaries while others keep their primary election open to party members and voters with "No Party Preference." To vote in the Republican, Green, and Peace and Freedom presidential primaries on June 7, voters must register with those parties by May 23.

If voters didn't list a party preference on the ballot, they will still be allowed to vote in the Democratic, American Independent, or Libertarian parties. However, a Los Angeles Times investigation found that nearly three-quarters of registrants in the "ultraconservative" American Independent party may have mistakenly registered thinking that it indicated having no party preference. Any voters registered with the American Independent Party will be limited to voting for candidates within that party unless they re-register by the May 23 deadline.

Voters can register to vote with a party online here.

Proposition 50

Aside from assorted municipal ballot measures, the main legislative issue before voters throughout California will be whether to allow the State Senate and Assembly to suspend legislators without pay and benefits. Currently, the legislature can suspend members with a two-thirds vote in either the Senate or Assembly, but doing so doesn't suspend legislators' pay and benefits.

The measure passed in the state Senate 31–3 and the Assembly 73–2.

A "yes" vote would approve a state constitutional amendment to allow the suspensions. Advocates say that the measure would increase disciplinary authority and accountability, while critics fear that the measure could be used to stifle political opposition and decrease representation because voters are left without active representation in the legislative body if the legislator is suspended and re-elections cannot be held.

Expulsions are rare, and the California Legislative Analyst's Office wrote that the most recent one occurred in 1905.

Contentious Senate, Supervisor Races

Open primaries will be held for a variety of offices, including U.S. senators and congresspeople, state senators and assembly members, county supervisors, and Superior Court judges.

The most high-profile race is for U.S. Senator Barbara Boxer's seat, the first open California Senate seat since 1992. The top two vote-getters in the primary, regardless of party, will advance to the ballot in November.

The Capitol Weekly reported that it is likely that two Democrats, California Attorney General Kamala Harris and U.S. Rep. Loretta Sanchez (D–Santa Ana) could end up on the ballot in November. The two led in the most recent USC Dornsife/Los Angeles Times poll, but a full one-third of voters are still undecided.

Statements from the over 20 Senate candidates are available here.

In Los Angeles County, there's a hotly contested race to replace Los Angeles County Supervisor Michael Antonovich, who is reaching his term limit. Antonovich has served for nearly 35 years. Eight candidates are on the primary ballot to take his place.

According to the Los Angeles Times, members of the Board of Supervisors have significant power because each one represents around 2 million people, and the board as a whole is in charge of a $27 billion budget.

How to Vote

There are a few different options for how to vote in the primary elections, but some require voters to meet deadlines well in advance of June 7.

The first option is to vote by mail. Ballots must be requested from the County Registrar-Recorder/County Clerk's office by May 31 and postmarked at the latest by June 7.

Voters in Los Angeles County can also vote early in person at the Registrar-Recorder/County Clerk building in Norwalk starting 29 days before the election.

On Election Day, polls will be open from 7 a.m. to 8 p.m. Voters can find their local polling station online here.

For other comprehensive details on the primary voting process, the full voter information guide for Californians is available here.

Reach Staff Reporter Rachel Cohrs here, or follow her on Twitter.