Live election 2024 updates in the Philadelphia region and the focus on Pennsylvania

A small group of 10 to 12 voters lined up outside the Elections Office inside Philadelphia's City Hall on Monday afternoon.

Most of them were holding a single sheet of paper that would ensure their vote was counted. Voters filled out that paper to request a new ballot after not receiving theirs.

"I didn't want to take a chance. This election is too important," said Novilette Jones of Somerton.

Other voters found out there were issues with their ballots that needed to be corrected.

Lauren Cristella, president and CEO of the non-partisan group Committee of 70, says several errors can lead to a ballot being flagged.

Has your mail-in ballot been flagged? Here's how to find out

"There are a few different ways that people can make a fatal flaw on their mail-in ballot. One of them is forgetting to sign it. Another is dating it incorrectly or not dating it at all," she said. "The other is to not use the secrecy envelope."

Officials in Philadelphia say they still have about 1,800 ballots with errors that need to be fixed.

The 6abc data team found Chester County has 388 ballots with errors. In Montgomery County, there were 240 as of Monday afternoon.

"I recommend everyone go to montcovotes.com to check the status of their ballots -- you can look it up. You just need your birthdate, your name, and your ZIP Code," said Montgomery County Commissioner and Board of Elections Chair Neil Makhija.

The Montgomery County Commissioner says voters who made mistakes still have time to cast a correct ballot.

It's up to voters to find out if their ballot has any issues.

"We encourage everyone who voted by mail to go to the Department of State's tracker, www.pa.gov, then right in the middle of the page it says mail ballot tracked," said Cristella.

Officials in several counties across Pennsylvania continue to investigate potentially fraudulent voter registration applications, as Trump has pushed some misleading or false claims about the incident.

Authorities in Lancaster, Berks, Monroe and York counties are investigating thousands of voter registration applications they say are potentially fraudulent, according to various officials around the state. Amid the ongoing investigations, some of the applications have been confirmed to be fraudulent while some have been determined to be legitimate, according to updates.

Still, as recently as last week Trump said Lancaster County was "caught ... with 2,600 votes."

"They found, as I understand it, I mean, I don't know what's happened to the last day or so, but they in Lancaster, they found 2,600 ballots, all done in by the same hand," Trump said Sunday in Pennsylvania.

But, according to the Pennsylvania attorney general, Trump's characterization is untrue. In a statement last week, the state's top prosecutor, Michelle Henry, said that "the investigations regard voter registration forms, not ballots."

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The power of the next president will be, in large part, determined by the makeup of Congress, especially the Senate, which approves cabinet positions and judicial nominations.

Senators also can set or defeat a president's legislative agenda.

There are 34 seats up for grabs, and the fight for control of the chamber is coming down to a handful of races. Among those is Pennsylvania, where incumbent Democrat Bob Casey is locked in a bitter and expensive battle with Republican Dave McCormick.

Breaking down Pa. Senate race between Casey, McCormick

"What we're probably going to see is that whoever wins the presidency is also their party's candidate for the Senate will also be the winner," said Professor Ben Dworkin of Rowan University Institute for Public Policy and Citizenship.

McCormick spoke at a Donald Trump rally in Reading Monday afternoon, hoping the top ticket will bring votes down the ballot.

"The choice for your Senate, President Trump needs a majority in the Senate. He needs a strong leader from Pennsylvania to get our country back on track. The choice between me and Bob Casey couldn't be more clear," McCormick said.

In the weeks leading up to the election, both candidates have highlighted their broad differences across issues like energy, abortion rights and the economy.

Bob Casey held a rally in Warrington alongside Senator Cory Booker.

"When you look at some of the numbers in the last couple of election cycles, the percent of the vote that a candidate gets in this county is very close to what they get statewide. So no pressure right," Casey said.

The outcome of this race is now dependent on Pennsylvanians.

Vice President Kamala Harris continued her Monday swing through Pennsylvania with a rally targeted in large part at Puerto Rican voters in Allentown, a majority-Latino city.

It's where the Harris campaign sees an opportunity to woo voters turned off by the racist joke Tony Hinchcliffe told at former President Donald Trump's New York rally last month.

When Mayor Matthew Tuerk mentioned Hinchcliffe's "garbage" comment, the crowd at the Muhlenberg College gymnasium booed, and at least two Puerto Rican flags were unfurled.

Rapper Fat Joe, who spoke shortly before Harris, called upon Latino voters to have "pride" and reject Trump.

"They said they needed a Puerto Rican in Allentown, and I was more than honored to come speak to my people," he said.

In her own remarks, the vice president touted her "long-standing commitment to Puerto Rico and her people."

She promised that she would be "a president for all Americans" and added that her campaign has "momentum" in the closing hours of the race.

"It is my pledge to you, if you give me a chance to fight on your behalf as president, there is nothing in the world that will stand in my way," Harris said.

-ABC News' Will McDuffie, Gabriella Abdul-Hakim and Fritz Farrow