As several key contests across the U.S. remain close, President Donald Trump has zeroed in on Florida, making a slew of unsubstantiated claims about "forged" ballots and "found" votes.

"When will Bill Nelson concede in Florida? The characters running Broward and Palm Beach voting will not be able to “find” enough votes, too much spotlight on them now!" Trump tweeted on Tuesday.

When will Bill Nelson concede in Florida? The characters running Broward and Palm Beach voting will not be able to “find” enough votes, too much spotlight on them now! — Donald J. Trump (@realDonaldTrump) November 13, 2018

There is no evidence of widespread fraud or forged ballots in the state, election observers and law enforcement said.

On Monday, Republican Gov. Rick Scott's Senate campaign sought a mandatory injunction to impound voting machines that were not being currently reviewed in Broward County, but a judge shot him down, noting that there was no evidence of voter fraud of irregularities.

"I don't think I have any evidence to enter a mandatory injunction right now," Judge Jack Tuter said.

"If someone in this lawsuit, or someone in this county has evidence of voter fraud or irregularities at the supervisors office, they should report it to their local law enforcement officer," he added. "If the lawyers are aware of it, they should get the person to swear out an affidavit, but everything the lawyers are saying out there in front of the elections office is being beamed all over the country. We need to be careful what we say."

Let's take a look at Trump’' more specific claims and the facts.

Claim: Ballots "out of nowhere," missing and forged

"The Florida Election should be called in favor of Rick Scott and Ron DeSantis in that large numbers of new ballots showed up out of nowhere, and many ballots are missing or forged," Trump wrote in a tweet.

A large number of ballots did not show up out of nowhere; they came in the mail.

Some 2.5 million Floridians voted requested mail-in ballots this election, and many of them were delivered back to election administrators on Election Day. Those are typically counted after polls close on Election Day, and counting a single ballot can take days if there are any problems.

Counting mail-in ballots takes a lot of time, according to Ion Sancho, a retired 28-year veteran elections supervisor from Leon County, Florida, and a key election expert in the 2000 presidential race election recount.

The Florida Election should be called in favor of Rick Scott and Ron DeSantis in that large numbers of new ballots showed up out of nowhere, and many ballots are missing or forged. An honest vote count is no longer possible-ballots massively infected. Must go with Election Night! — Donald J. Trump (@realDonaldTrump) November 12, 2018

First, signatures on the outside of an envelope must be verified before the ballot is opened and the vote counted. If there is anything wrong with the paper ballot — a paper tear or bend that prevents it from scanning properly — the ballot must be duplicated by hand, checked by another person, and verified by a three-person panel before it is counted.

Since expanding the use of mail ballots after the 2000 election, Florida did not change their deadlines for certifying election results, something that puts election officials under enormous pressure, according to Sancho, who recalls falling asleep sitting upright doing this work.

"The problem is not fraud; the problem is legislatively drawn timelines," Sancho told NBC News.

Claim: "honest vote count is no longer possible"

"An honest vote count is no longer possible-ballots massively infected. Must go with Election Night!” Trump continued in the same tweet.

Not according to election experts.

Despite the vote counting process taking time, Sancho said there are provisions are in place to keep vote counts from being corrupted.

"Every elections office has a secure area with security where ballots are stored. Voter ballots are stored in one area, blank ballots are stored in another area. We are very security conscious," he said.

What's more, election night results will never be used despite Trump's assertion, Sancho noted. The first official results are the ones counted by noon on the Saturday after an election.

Election workers place ballots into electronic counting machines, on Nov. 11, 2018, at the Broward Supervisor of Elections office in Lauderhill, Florida. The Florida recount began Sunday morning in Broward County. Joe Cavaretta / South Florida Sun-Sentinel via AP

Claim: Scott's margin shrunk due to nefarious activity

"Rick Scott was up by 50,000+ votes on Election Day, now they “found” many votes and he is only up 15,000 votes. "'The Broward Effect.' How come they never find Republican votes?" Trump wrote in another tweet.

Scott did lead by a strong margin on election night, but as mail-in and provisional ballots continued to be counted — particularly in Democratic-leaning Broward County — his margin shrunk.

"These are not found ballots, they are ballots that were not processed until after the Election because they came in the day of the election!" Sancho said.

While problems and irregularities have been reported — including 22 ineligible ballots that were mistakenly counted, for instance — there's no evidence of any kind of criminal meddling.

Broward County is an easy target for Republicans crying fraud. A federal judge ruled this spring that election administrator Brenda Snipes violated state and federal laws by destroying paper ballots from a 2016 primaries too soon, and ordered two election monitors to watch over Snipes' handling of the 2018 election.

"Our staff has seen no evidence of criminal activity at this time," a Department of Elections spokesperson told the Miami Herald this weekend of the monitors. Florida's Department of Elections is within the Florida Department of State, which is led by a Scott appointee.

The Florida Department of Law Enforcement official told NBC News on Friday that they are "not actively investigating" any voter fraud right now.

Claim: Palm Beach County's 'characters' are a problem, too

Trump's Tuesday tweet also cited another left-leaning urban county, Palm Beach County, as a problem.

"The characters running Broward and Palm Beach voting will not be able to 'find' enough votes, too much spotlight on them now!" he wrote.

Sancho said Palm Beach's problems are not because of their current staff: Despite requests for funding to buy new voting machines, the third-largest county is saddled with outdated voting machines that can only process one race at a time, something that will make meeting the state's recount deadlines almost impossible.

"It's an incredible nightmare. Every county besides Palm Beach can feed all the ballots through the sorters and the sorters can program and (process) all three statewide races at onetime, except Palm Beach which is going to have to feed all 600,000 of their ballots separately for each recount," he said. "All bets are off."

Sancho said the statewide deadlines are simply too short, and other states with mail-in ballots have much longer period for election staff to certify election results: California has 28 days, he told NBC News, "which is why they do it pretty well!"