CONCORD, N.H. -- White House hopefuls have been flocking all year to the state that holds the first primary in the race for the White House.

But this is when New Hampshire’s primary gets real.

Starting Wednesday, the presidential candidates will begin trekking to the New Hampshire secretary of state’s office on the second floor of the historic State House in Concord, as the two-and-a-half-week-long filing period for the primary gets underway.

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"The filing period is the starter's gun for the home stretch of our first-in-the-nation primary,” explained Jim Merrill, a longtime New Hampshire-based GOP consultant and veteran of the George W. Bush, Mitt Romney, and Marco Rubio presidential campaigns.

While this quadrennial tradition in New Hampshire usually follows the script, there’s a chance for some curveballs this time around. Among the top questions: Will Hillary Clinton – or even Mike Bloomberg – startle the political world by making last-minute trips to the Granite State by Nov. 15, the final day to file?

The odds for such a monumental surprise are extremely slim, but even without such breaking news, there will still be plenty of action grabbing national and even international attention.

The candidates stop at the secretary of state’s office to meet with longtime Secretary of State Bill Gardner, known across the country as the state official who’s led the charge for decades to keep New Hampshire’s cherished primary tradition alive. The candidates pay their $1,000 filing fee and sign paperwork to have their names placed on the primary ballot.

“It’s a time when the center of the American political universe shrinks to the size of Bill Gardner’s office,” noted University of New Hampshire political science professor Dante Scala, a longtime primary commentator.

Some of the candidates running for the White House have been paying visits to the Granite State for well over a year -- or in former Rep. John Delaney of Maryland’s case, the summer of 2017. But with just three-and-a-half months to go until the February primary, the campaign now reaches prime time.

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The filing is much more than a clerical event. The larger campaigns will hold rallies outside the State House and pack the second-floor corridor leading to the secretary of state’s southwest corner offices with supporters. Dozens of reporters and photographers will squeeze into the small offices to capture the moment and, by tradition, the candidates will then take questions from the media.

“Even after months of campaigning, the whole thing becomes more real when the candidate walks through Bill Gardner’s door,” Scala said.

And Merrill noted, “It's a time when frontrunners, fringe candidates and everyone in between gets a chance to place their name on the ballot in the crowded mayhem of Bill Gardner's corner office.”

But more importantly, he emphasized that “it also marks a new phase of the primary when campaigns begin to sprint here and we really begin to see which candidates are built to last, and which ones are destined to falter."

South Bend, Ind., Mayor Pete Buttigieg will make the trek to the State House on Wednesday, on opening day. Sen. Bernie Sanders of Vermont – who easily won the 2016 Democratic presidential primary in New Hampshire – files the following day. Both are holding rallies for supporters following their filings.

The filing period comes amid some speculation that 2016 Democratic presidential nominee Hillary Clinton may be seriously mulling a third stab for the White House.

Clinton’s own comments and actions in recent weeks sparked the buzz, fueling stories that she could possibly enter her party’s nomination race at this late date amid complaints from some Democratic Party insiders who view the current field of contenders too weak or progressive to take on Republican President Trump next year.

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But a top Granite State Democrat says concern with the field and a hunger for another candidate is not a topic of conversation that she's heard.

“I’ve heard nothing about people wishing someone else would get into the race,” said Kathy Sullivan, a longtime Democratic National Committee member and former New Hampshire Democratic party chair.

Sullivan, who backed Clinton in the 2008 and 2016 presidential campaigns, told Fox News “I’m not taking this seriously. I love Hillary Clinton and I think she’d be a fantastic president but there is a lot of really good people running for president right now. I think it’s too late in the day for someone to get into the race.”

There’s also some speculation regarding former New York City Mayor Michael Bloomberg, who visited New Hampshire last winter before ruling out a 2020 White House run.

The billionaire media mogul, philanthropist, and environmental and gun control advocate took aim at the current field of Democratic contenders at a political event Monday in Washington, D.C.

"I have my reservations about the people running and their campaigning, the promises they're making that they can't fulfill and their willingness to admit what is possible and what isn't and their inconsistency from day-to-day,” he said as he chided the White House hopefuls.

An adviser to Bloomberg declined to answer when asked if Granite Staters should expect a visit by the former mayor during the primary filing period.

And then there’s former two-term Republican Gov. John Kasich of Ohio. There’s still some speculation that Kasich – a very vocal Trump critic who’s never ruled out primary challenging the president in 2020 – might visit the State House during the filing period.

Kasich returns to New Hampshire on Nov. 7 to give a speech at the University of New Hampshire in Durham as part of his latest book tour. But two top New Hampshire advisers to the 2016 GOP presidential candidate who came in second to Trump in the primary tell Fox News that there are no plans during the trip for Kasich to make the drive from Durham to Concord.

On the same day Kasich’s in New Hampshire, Vice President Mike Pence will head to the State House to file on behalf of his boss, President Trump.

High-profile surrogates have often filed for sitting incumbent presidents in past cycles. Then-Vice President Joe Biden filed in 2011 on behalf of President Barack Obama in the 2012 primary. And then-First Lady Hillary Clinton made the trip to Concord in 1995 to file to put her husband, President Bill Clinton, on the 1996 primary ballot.

For Pence, the trip may also be about the next presidential election.

Merrill noted that "this is a perfect example of a happy convergence of interests for Vice President Pence -- serving in his traditional role as VP converging with his very real interest in getting attention and making friends in NH for his eventual campaign for the presidency in 2024, which will begin approximately five minutes after Election Day in November 2020."