CONCORD, N.C./WINTERVILLE, N.C. (Reuters) - Hillary Clinton’s supporters nervously eyed opinion polls showing the Democrat with a tenuous lead over Republican rival Donald Trump on Thursday as the White House candidates raced through vital battleground states in a late search for votes.

The race for the Oval Office has tightened significantly in the past week, as several swing states that Trump must win shifted from favoring Clinton to toss-ups, according to the Reuters/Ipsos States of the Nation project.

The project, a survey of about 15,000 people every week in all 50 states plus Washington, D.C., found the two candidates were now tied in Florida and North Carolina and that Clinton’s lead in Michigan had narrowed so much the state was too close to call. Ohio remained a dead heat, with Pennsylvania now tilting to Clinton.

A Reuters/Ipsos national daily tracking poll found on Wednesday that Clinton was leading Trump by 6 percentage points, the same advantage she held before FBI Director James Comey sent a letter to Congress last week saying the agency had found a new cache of emails potentially related to its probe of Clinton emails.

Other polls have shown a far closer race, fueling Democratic worries about the state of the race just five days before Tuesday’s election. Clinton’s national lead over Trump eroded to 3 percentage points among likely voters in a New York Times/CBS News poll on Thursday, down from 9 points just two weeks ago.

An average of polls compiled by the RealClearPolitics website also showed her lead at 1.7 percentage points on Thursday, well down from the solid advantage she had until late last month.

“I’m worried that Trump may win,” said Nancy Dubs, 83, a retiree in Pittsburgh, who said she was voting for Clinton. “I think it’s maybe time to have a female president.”

For Clinton supporters, it has been a quick shift from confidence to anxiety.

“I think all of us are a little bit nervous,” said Rajnandini Pillai, a professor at California State University at San Marcos, who plans to back Clinton. “It seemed pretty much in the bag a couple weeks ago.”

Nevertheless, some polls showed Clinton recovering slightly from her slide in the past week. She has maintained her comfortable edge in the Reuters/Ipsos poll and inched back into a 2-point lead over Trump in the latest Washington Post-ABC News tracking poll, which had shown Clinton falling slightly behind Trump earlier this week.

President Barack Obama, on the third day of a multi-state campaign trek for Clinton, adopted a sense of urgency before a raucous crowd at Florida International University.

“You have the chance to shape history,” Obama said. “There are times where history is ... moveable. Where you can make things better or worse. This is one of those moments.”

The tightening White House race has rattled financial markets as investors weigh a possible Trump victory. Investors have generally seen Clinton as the candidate who would maintain the status quo, while there is more market uncertainty over what a Trump presidency might mean in terms of economic policy, free trade and geopolitics.

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Global equity prices drifted lower on Thursday as worries about the election weighed on investor sentiment.

FOCUS ON BATTLEGROUND STATES

With the White House race decided on the Electoral College system of tallying wins on a state-by-state basis, Clinton and Trump are focused on a handful of battleground states. Trump began the day in Florida before heading to North Carolina for two rallies. Clinton was in North Carolina for two rallies.

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Florida and North Carolina are both must-win states for Trump as he tries to piece together the 270 electoral votes needed to capture the White House. Clinton, who has comfortable leads in big states such as California and New York, could more easily reach 270 votes without winning either Florida or North Carolina.

In Florida, Trump pressed his argument that the controversy over Clinton’s use of a private server for her email when she was U.S. secretary of state from 2009 to 2013 was part of a pattern of corruption that made her unfit for the White House.

Comey concluded at the end of a year-long FBI probe in July that there were no grounds to bring any charges. His brief letter advising Congress last Friday about the agency reviewing newly discovered emails said they might or might not be significant, but the news was seized on by Trump and other Republicans.

Republicans in Congress have already vowed to lead investigations of Clinton’s email practices and her family charitable foundation.

“She is likely to be under investigation for many, many years. Also likely to conclude in a criminal trial,” Trump said in Jacksonville.

At a later rally in Concord, North Carolina, he said that “the political leadership” at the Justice Department was trying to protect Clinton.

Trump’s wife, Melania, tried to bolster his standing with women during her first campaign-trail appearance, in a Philadelphia suburb.

“We must win on Nov. 8 and we must come together as Americans. We must treat each other with respect and kindness even when we disagree,” she said in Berwyn, Pennsylvania.

Trump, a New York businessman who has never previously run for political office, has called for a ban on Muslims entering the country, launched his campaign by calling illegal immigrants from Mexico rapists and was captured in a 2005 video that surfaced last month boasting of groping women and making other unwanted advances.

At a campaign rally in Winterville, North Carolina, a community where more than a third of the population is African-American, Clinton asked the crowd to imagine life under a Trump presidency.

“He has spent this campaign offering a dog whistle to his most hateful supporters,” she said. “I just don’t believe we’re at our best when we stoke fear about each other.”