JEFFERSON CITY — Missouri's presidential primary got off to a rough start Tuesday for some voters, as problems with electronic equipment in the state's most populous county led some people to give up and head to work without casting their ballots. 

Election officials in St. Louis County said their electronic poll books, which are used to check in people, had trouble syncing with their system. That meant they could not print out tickets, which are scanned to print out ballots for each voter. 

The problem was compounded when some poll workers failed to switch to a manual system to print ballots. 

"They got flustered," said Rick Stream, a Republican who is one of two election directors in St. Louis County. "Voters left, they had to go to work. That's on us, we should have had everything working properly."

It's unclear how many voters gave up. But the problems, which lasted for at least the first hour of voting, appeared widespread. Stream estimated that people had reported problems from at least 50 of the county's roughly 400 polling sites. He said problems could have occurred at more sites but just not been reported. 

Kansas City Mayor Quinton Lucas also reported voting problems in his city — with his own ballot. Lucas said he initially got turned away at his polling site because workers couldn't find his name on the voter registration list. He said it turned out that his name had been entered backwards — with his last name listed as his first name. 

Missouri is among several states holding presidential primaries on Tuesday. Former Vice President Joe Biden was looking to build upon the momentum from last week's primary victories in what has become essentially a head-to-head battle with Vermont Sen. Bernie Sanders. 

But Missouri has a recent history of close Democratic primaries. In 2016, Sanders lost by fewer than 2,000 votes to eventual Democratic presidential nominee Hillary Clinton.

Voters were urged to take extra precautions Tuesday because of concerns about the new coronavirus. Some polling places provided hand sanitizer for voters and stocked up on disinfectant wipes for the equipment and pens. Others encouraged voters to bring their own pens to mark their ballots.

Whoever wins the Missouri primary faces an uphill battle to carry the state in November against Republican President Donald Trump. The last Democrat to carry Missouri was President Bill Clinton, in 1996. Barack Obama narrowly lost in Missouri in 2008, but the state has turned decidedly Republican since then. Mitt Romney carried Missouri by 9 percentage points in 2012, and Trump won the state by 19 percentage points on the way to victory in 2016.

Missouri was long considered a bellwether state until the recent trend. Missouri voted for the winning presidential candidate every time but once in the 1900s, missing only in 1956 when it picked Democrat Adlai Stevenson instead of Republican President Dwight Eisenhower.

Idaho, Michigan, Mississippi, North Dakota and Washington also were holding presidential primaries Tuesday. 

Biden started as the early front-runner nationally but was declared all but finished before rebounding with a much stronger than expected showing during last week's elections.

Biden and Sanders have been largely cordial. Biden, without naming Sanders, has taken aim at Sanders' frequent contention that Biden is beholden to the party establishment.

Sanders, at a rally in St. Louis on Monday, shot back at those who say Biden is more electable, saying it's the enthusiasm and excitement of his campaign that will bring out more voters in November to defeat Trump.

University of Missouri-St. Louis political scientist Dave Robertson said a surge toward Biden in the Midwest could indicate good things for the Democrats in November "because we might get a pattern with white working-class voters coming back to the Democrats to some extent." 

"If Biden has a pretty big margin and it's a big-time vote, it could indicate that white working-class voters are coming back to a moderate in the Democratic Party," he said.

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Salter reported from St. Louis. Associated Press writer Heather Hollingsworth in Kansas City contributed to this report.