So you want to run for US president.

You'll need some ideas, a supportive team and a good slogan. Plus some money.

So. Much. Money.

But how much exactly? Let's find out.

To begin with, you need at least $US5,000

America's Federal Election Commission will recognise you as a candidate if you've raised or spent $US5,000 and filled in the necessary forms. As of right now, 458 Americans have done just that (including candidates Chocolate Pancakes and Jo 753. Really.)

But if you want to win? It's going to cost a lot more than that.

In 2016, more than $US2 billion ($2.5 billion) was spent on presidential campaigns according to the Center for Responsive Politics, a nonpartisan group that tracks money in US politics.

Outreach Manager Brendan Quinn says it's tricky to narrow down an exact figure of how much any given candidate will need because running for president keeps getting more expensive.

"All federal races, cycle to cycle, have been increasing in costs. The midterms in 2018 broke records for congressional races through both the House and Senate," he said.

In short, you're probably going to need more than the last people who ran. To give you a rough idea, in 2016 Hillary Clinton raised $US585,699,061 (with $US206,122,160 in outside money), Donald Trump $US350,668,436 (with $US103,951,568 in outside money).

"We absolutely expect 2020 to far surpass [that], even adjusting for inflation," Mr Quinn said.

You'll need to learn to like fundraising dinners

Because presidential candidates attend a lot of them. Mayor Pete Buttigieg, a democratic candidate, famously attended five Silicon Valley fundraisers on a single Friday night.

But those glitzy affairs are only one of the many ways candidates build up their campaign war chests. Others include:

Ticketed events

Ticketed events Cheques in the mail

Cheques in the mail Donations from political action committees (PACS)

Donations from political action committees (PACS) Campaign merchandise

That last item, the merchandise, is just one of the many ways candidates are getting creative in order to stand out in a crowded field.

Elizabeth Warren has leveraged her pooch, a golden retriever named Bailey, to sell government-themed dog collars and bandanas. Joe Biden is peddling a coffee mug that reads (drumroll please) "Cup o' Joe".

This dog collar, a throwback to Elizabeth Warren's role in establishing the Consumer Financial Protection Bureau, costs $US23. ( Reuters )

And pretty much every candidate offers a hat, presumably so voters can take a sartorial stand against the ubiquitousness of those red "Make America Great Again" lids.

A $US25 hat may seem trivial, but those merchandise sales add up fast. According to digital agency Revolution Messaging, Bernie Sanders raised more than $US15 million from merchandise during his unsuccessful 2016 bid.

Those smaller online donations from individual voters are becoming even more popular in the lead-up to the 2020 election.

One reason? It's easy.

"It's really, really good for President Trump, who can have these people that see him in a commercial, or make TV appearance … and immediately make a contribution," Mr Quinn said.

Another reason? It gives candidates street cred in the long battle to reform how corporate money influences American politics.

How do you spend all that money?

Early in the cycle, there's one thing candidates spend the majority of their money on.

"Most of the money is focused on getting more money," Mr Quinn said.

"After they stop spending money to make money, they start spending money to get their real messages out there."

Rachel Curley is a democracy associate for non-profit advocacy organisation Public Citizen's Congress Watch division.

She said money is also spent to help build the huge infrastructure needed to run an effective presidential campaign.

NBC reported that in 2016 at least 4,200 people worked on Hilary Clinton's campaign. Nearly 900 worked on Donald Trump's.

"A lot of it goes to traditional campaign operations staffing up the field, you know a bunch of folks who are knocking on doors, who are setting up town halls. All of the logistics that go into a campaign machine," she said.

"I mean our elections here are so long that they have to sustain campaign operations for months."

Senator Kamala Harris speaks at a campaign house party in New Hampshire. Candidates will attend hundreds before a vote is even cast. ( Reuters: Brian Snyder )

On money in politics, American voters are forcing change

As they rake in money from hats and dog collars, a number of Democratic candidates for 2020 are swearing off donations from corporate PACS. Ms Curley said plenty of candidates did the same at the 2018 midterm elections — and voters rewarded them.

"Candidates ran on the premise that rejected corporate PAC money and won in the midterm elections," she said.

According to a 2018 Pew Research Center report, 77 per cent of Americans say there should be limits on the amount of money individuals and groups can spend on campaigns and 65 per cent want new laws to reduce the role of money in politics.

Ms Curley said the For The People Act, which among other things limits spending on political campaigns and establishes a system of public funding for elections in some federal offices (similar to the system used for Australian elections), is the closest Congress has come to forcing reform.

It passed the House of Representatives in March, but is unlikely to ever come to a vote in the Republican-controlled Senate.

This is all-important. Because whoever raises/spends the most money wins …

… usually.

According to OpenSecrets, in the 2018 midterm elections the candidate who spent the most money won in 88.8 per cent of races in the House, and in 82.9 per cent of races in the Senate.

But there are exceptions to the rule when it comes to the presidency.

In 1996, Bill Clinton raised far less than his opponent, Bob Dole. And in 2016, Donald Trump raised far less than Hillary Clinton.

But President Trump is taking no chances in his bid for re-election.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 9 seconds 2 m 9 s Trump delivers an expansive speech at his 2020 campaign launch.

"President Trump made the unprecedented move to file for re-election the night he was inaugurated, which no president in history has done. So he's been raising funds since January 2017 and he has a ridiculous amount of money in his war chest right now," Mr Quinn said.

How much is "ridiculous"?

According to the latest disclosures, Mr Trump has raised $US135,600,000 so far. The closest Democrat? Bernie Sanders, who's banked $46,300,000.

That vast gap doesn't mean that Mr Trump has already won re-election in 2020.

Ms Curley is adamant that in a US political landscape that has bucked conventional wisdom since 2016, raising eye-watering amounts of money may not be as important as a candidate's position on the issue.

"That message of democracy reform, and the message of rebalancing our democracy and giving the power back to the people, is a really powerful one," Ms Curley said.