Bernie Sanders just won't go away -- and that's a growing problem for Hillary Clinton and the Democratic Party as the front-runner once again failed Tuesday to score the decisive victory needed to put the Vermont senator in her rear-view mirror and turn her full attention to Donald Trump.

Sanders easily beat Clinton in the Oregon Democratic primary, and was running neck-and-neck with her in Kentucky, though Clinton claimed victory with less than 2,000 votes separating them and not all precincts counted.

“I say to the leadership of the Democratic Party, open the doors, let the people in,” Sanders said, alluding the Kentucky's voting format which allowed only registered Democrats to vote.

Should Clinton pull out a win in Kentucky, the closeness of the race and her loss in Oregon still prevents her from doing a full pivot to a November general election matchup with Donald Trump, the presumptive Republican nominee.

With 99 percent of the precincts reporting in Kentucky, Clinton led Sanders by just over 1,900 votes out of more than 423,000 that were cast.

“We just won Oregon, and we’re going to win California,” the Vermont senator told supporters in Carson, Calif., where he vowed to “take our fight” to July's Democratic National Convention in Philadelphia.

Sanders' victory was his 21st of the election cycle and his 11th in the past 17 contests. The win also broke Sanders' streak of eight straight losses in so-called "closed primaries", where only registered Democrats can vote.

The Kentucky Secretary of State's office reported that Clinton led Sanders 46.8 percent to 46.3 percent with 100 percent of the votes in. The Sanders campaign did not immediately say whether it will challenge the results in Kentucky, which does not have an automatic recount.

According to an Associated Press tally, Clinton and Sanders each received 27 of Kentucky's 55 Democratic delegates, with one delegate to be awarded to the statewide winner. In Oregon, Sanders had won at least 28 of the Beaver State's 61 Democratic delegates, with Clinton winning at least 24 and nine other delegates outstanding.

Clinton currently has 2,291 pledged delegates and superdelegates to Sanders' 1,528. She requires a total of 2,383 to clinch the Democratic nomination.

Clinton repeatedly tried to turn the focus to Trump while campaigning in Kentucky over the weekend, calling the billionaire real estate mogul a "loose cannon" and saying she had "never heard such reckless, risky talk from somebody about to be a nominee for president than I’ve heard from Donald Trump when it comes to nuclear weapons."

For his part, Trump taunted Clinton on Twitter shortly after the polls closed in Kentucky Tuesday night.

In Oregon's Republican primary, Trump faced no active opposition in winning 67 percent of the vote. Ohio Gov. John Kasich and Texas Sen. Ted Cruz received 17 and 16 percent of the vote respectively, as more than 104,000 ballots were cast for Trump's former rivals.

Trump won at least 17 of Oregon's 28 Republican delegates, with Cruz and Kasich each receiving at least three and five other delegates outstanding. Trump now has 1,160 delegates, just 77 away from the threshold needed to clinch the GOP nomination.

The Associated Press contributed to this report.