Voters in two states -- Kentucky and Oregon -- are casting their ballots in the Democratic or Republican races for president. Kentucky is only holding a Democratic party since it held Republican caucuses on March 5. Oregon, on the other hand, is holding primaries for both political parties.
Hillary Clinton and Bernie Sanders are the main candidates on the Democratic ballot. Donald Trump is now the presumptive GOP nominee.
Watch CBSN at 7 p.m. ET for coverage of the Republican and Democratic primaries
Polls are open in Kentucky at 6 a.m. ET/CT, and polls there close at 6 p.m. ET/CT (part of the state is in the Central Time Zone -- those polls close at 7 p.m. ET). ballots in Oregon must be received by 8 p.m. PT / 11 p.m. ET.
Both Kentucky and Oregon operate under closed primary systems in which only registered voters of each party can cast ballots in their respective primaries.
While Kentucky voters vote at traditional polling sites, no polls are actually open in Oregon. Instead, voters mail their ballots in via snail mail. Ballots were sent out two to three weeks before the primary and are due back by 8 p.m. PT. Last-minute voters can also drop their ballots off at designated locations. As of last Thursday, 564,804 ballots had been returned.
In the Republican race, 28 delegates are up for grabs in Oregon and most are distributed proportionally -- one delegate for every 4 percent of the statewide vote.
In the Democratic race, 55 delegates will be available in Kentucky and they will be allocated proportionally among candidates that get 15 percent or more of the vote statewide. In Oregon, 61 delegates are up for grabs and most will be allocated the same way.
In 2008, Clinton defeated then-Sen. Obama in Kentucky's Democratic primary. Mr. Obama, on the other hand, won Oregon. In 2008 and 2012, John McCain and Mitt Romney, respectively, won the Kentucky and Oregon primaries.
The primaries come just days after the Nevada Democratic state convention erupted into chaos, which involved some chair-throwing by Sanders supporters. In the Republican race, meanwhile, efforts are underway to draft a third-party candidate to derail Trump, the presumptive GOP nominee.
He's not the official nominee yet. According to CBS News' latest count, Trump has 1,133 delegates and needs 1,237 delegates to clinch the nomination. Clinton has picked up 2,239 delegates, including superdelegates, and Sanders has 1,462. In the Democratic race, a candidate needs 2,383 delegates to win the nomination.
There are only three more primary days left -- May 25, June 5 and June 7. The remaining states are Washington, Puerto Rico, California, Montana, New Jersey, New Mexico, North Dakota and South Dakota.
→What: Democratic and GOP primaries in Oregon, Democratic primary in Kentucky
→ CBSN election coverage begins at 6 p.m. ET
→ Where: Kentucky, Oregon
→ When: Polls will be open in KY from 6:00 a.m. ET/CT to 6:00 p.m. ET/CT (polls in Central Time Zone close at 7 p.m. ET) and voters must mail their ballots in by 8 p.m. CT in OR.