The coronavirus pandemic could pose big problems for the two marquee political events before Election Day — the Democratic and Republican national conventions this summer.

Party leaders are being forced to consider the possibility that the four-day gatherings may have to be dramatically scaled back or essentially cancelled, while the candidate nominating process and fundraising tens of millions of dollars for the events could be severely hampered, former convention officials told NBC News.

The economic impact on the host cities — Milwaukee for the Democrats on July 13-16 and Charlotte for the Republicans on August 24-27 — could be devastating. While the economic benefit for both 2016 conventions fell short of some projections, the GOP's Cleveland effort generated $142 million while in Philadelphia, the Democratic event brought about $231 million.

The conventions are still far enough down that both parties are still planning for them to start on time. But the unpredictability of the outbreak — New York City Mayor Bill de Blasio said his city's major arenas may be closed for months — could leave organizers scrambling for alternatives in the not so distant future.

And the 2020 race has already become a non-contact campaign — Joe Biden and Bernie Sanders have switched into "virtual" campaign mode, forgoing large events and Sunday's Democratic debate will not have a live audience.

The first issue to pop up for the national conventions has been the postponement of some state party conventions, the process by which certain state parties choose the delegates who will represent their states at the national conventions.

In an email to state party chairs on Thursday, DNC chairman Tom Perez said the committee's delegate selection team has been in contact with states that are contemplating changes to their delegate selection process in light of the coronavirus outbreak to ensure the candidate nominating process "can continue without major interruptions."

But that's not the biggest worry on the horizon for organizers, who, should the crisis fail to pass by the summer, could be pressed with having to make major changes to their plans, such as shortening the four-day conventions, holding them with only delegates in attendance or even going as far to stage a virtual nominating process.

The gatherings are large. The 2016 Republican National Convention pulled in about 44,400 visitors, according to a Cleveland State University study. Meanwhile, estimates for that year's Democratic National Convention were similar, with about 50,000 estimated to have attended.

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Past organizers said the biggest issue on the immediate horizon involves the vast fundraising of millions of dollars to stage the events.

"A big part of what we did was raising money — this puts a lot of that in limbo," said Mike Dino, who served as CEO of the Denver host committee that helped organize the 2008 Democratic National Convention.

"And if you still want to bring all the delegates together, but you don't want anybody else there, as we're seeing in a lot of our public venues at this point, you don't have the people to pay for that that usually pay for that — the corporations that want to attend to be a part of that, too," Dino continued.

For the upcoming conventions, Democrats are slated to have 4,750 delegates present while Republicans will feature 2,550. Those totals do not include alternate delegates who would also be in attendance. Based on 2016 totals for both the Republicans and Democrats, there could be anywhere from 75 speakers to more than 250 delivering addresses at the nominating events.

"Raising the money, to at least do what they had envisioned, is only going to get tougher at this point," he added, noting that the committees may even have to ask Congress for funding in the range of $10 million to $20 million for each convention. Congress already approved $100 million late last year in security funding for the conventions, but any new ask would be in addition to that and for non-security purposes.

David Gilbert, president and CEO of the Cleveland host committee which helped organize the 2016 Republican National Convention, told NBC News that from a planning perspective "something like this really is uncharted territory."

Even if the conventions go forward but have to be downsized, a major impact will be felt by the local economies in Milwaukee and Charlotte, which would be unlikely to see the anticipated return on their investments.

"The communities go through what they do because of the significant return they get," Gilbert said. "In terms of visitors, media exposure, influencers coming to their community — and they would lose every bit of it. I mean, my heart really goes out to Charlotte and to Milwaukee right now."

If the conventions are dramatically scaled back or essentially canceled, Gilbert estimated the loss to the cities would be well into the hundreds of millions of dollars.

"A lot of the reasons these communities do it is also to have the eyes of the world on them," he added. "It's such a rare opportunity. When, otherwise, would cities, particularly cities like a Cleveland or a Milwaukee or a Charlotte — that are great cities or mid-sized cities — have 15,000 credentialed media in their community, and the byline is from that place? That's a hard pill to swallow if that's going to be lost."

At this point, Democratic and Republican officials said they closely monitoring the coronavirus outbreak but are focused on starting the conventions on time and holding them as long planned.

"We're still looking at planning a safe convention for everybody four months from now," a senior official on the Democratic National Convention committee told NBC News, adding they are "seriously monitoring" the crisis.

The outbreak, the official said, is being added to the "regular contingency planning that's part of planning for any convention."

Democratic convention CEO Joe Solmonese said his team is "in constant communication with the local, state, and federal officials responsible for protecting public health and security" as the "fluid" situation develops.

On the Republican side, Blair Ellis, the communications director for the GOP convention, said the organizers "prioritize the health and safety of delegates, media, community members, and staff and have full faith and confidence in the administration's aggressive actions to address COVID-19."

"As we move forward with planning, we remain in close contact with local, state and federal officials and we will continue to closely monitor the situation and work with all stakeholders and health authorities to ensure every necessary precaution is taken into account," she continued.

And what about the November election? If the outbreak doesn't abate, could it be postponed?

A 2004 Congressional Research Service report concluded that Congress has a better claim than the president when it comes to delaying the general election in the wake of a "sufficiently calamitous event." At the time of the report, the concerns were in the context of a possible terror attack.

"The power of Congress to protect the integrity of the presidential election, combined with its authority to set the time of election, would also seem to provide the Congress the power to postpone elections because of a national emergency," the report said.

Congress, the report said, could vote to "delegate" that power to the president.