Democratic presidential candidate Hillary Clinton speaks at a campaign rally at Kent State University, Oct. 31, 2016, in Kent, Ohio.
Democratic presidential candidate Hillary Clinton speaks at a campaign rally at Kent State University, Oct. 31, 2016, in Kent, Ohio.

National polls in the U.S. show Democrat Hillary Clinton with a narrow edge over Republican Donald Trump in the last week of the presidential campaign, but the reopened investigation into Clinton's emails from her tenure as secretary of state has added an uncertain element to their last dash for the White House.

Several national surveys Monday showed Clinton with a 1-to-3 percentage point advantage over Trump, and with the two candidates locked in tight races in several highly contested states that will decide the outcome and make one of them the country's 45th president. Other surveys still show Clinton with a more likely path to victory, which would make her the country's first female president.

FILE - FBI Director James Comey makes a statement
FILE - FBI Director James Comey makes a statement at FBI Headquarters in Washington regarding its investigation into Hillary Clinton's use of a private email server while secretary of state.

The long campaign, already filled with numerous twists and turns that have left both candidates with unfavorable ratings among voters, was jarred again when Federal Bureau of Investigation Director James Comey announced the new email probe, to look at thousands of emails found on the computer of the estranged husband of a key Clinton aide, Huma Abedin.

Investigators secured a search warrant and are now trying to determine whether they are related to Clinton's handling of national security material in her emails while she was the country's top diplomat from 2009 to 2013.

While Democrats denounced Comey's reopened investigation, Trump told a rally in Michigan that "it took a lot of guts" for Comey to take a new look at Clinton's emails. "What he did was the right thing." Trump said.

WATCH: Clinton talks about the timing

Clinton told cheering supporters in Ohio she is confident investigators will reach the same conclusion in the new probe as they did in examining previous emails. "There is no case here," she declared.

White House spokesman Josh Earnest said President Barack Obama, who has campaigned several times for Clinton and often disparaged Trump, would neither "defend nor criticize" Comey's action in reopening the investigation. Earnest said Obama believes Comey is "a man of integrity."

FBI probe

Comey had previously closed an investigation into Clinton's handling of the classified material in July, declaring that she was "extremely careless" in dealing with the documents but that no criminal charges were warranted. For her part, Clinton has said on numerous occasions that her use of a private, unsecured email server based in her New York home was a mistake, but that she did not knowingly send or receive classified material through the numerous electronic devices she used.

WATCH: Earnest on FBI Director Comey

Polls have shown little immediate impact from Comey's renewed investigation, which Democrats have attacked as politically motivated and an uncalled for, last-minute intrusion into the November 8 election that violated the FBI's long-standing tradition of avoiding any actions that might sway a political contest.

Meanwhile, Trump is trying to capitalize on the renewed look at Clinton's emails, which have cast a cloud over her candidacy from the start more than a year ago.

"Hillary Clinton is not the victim," Trump told a rally late Sunday in the southwestern state of New Mexico, where Clinton holds a solid lead. "You, the American people, are the victims of this corrupt system. When we win on November 8, we are going to Washington, D.C., and we are going drain the swamp."

WATCH: Trump on Comey doing "the right thing"

With polls showing that Clinton is leading in states that Democratic presidential candidates have traditionally carried, Trump is attempting in the last days of the campaign to flip several of these states to give him a better path to the White House.

Electoral College

U.S. presidents are not elected by the national popular vote, but rather by contests in each of the country's 50 states and the capital city of Washington, with the most populous states carrying the most weight in determining the overall outcome.

Trump's New Mexico and Michigan visits, as well as stops in Wisconsin and Pennsylvania on Tuesday, are all aimed at capturing states where surveys show Clinton ahead and poised to win their electoral votes. Both Clinton and Trump are searching for the majority of 270 or more of the 538 votes in the Electoral College.

Clinton is in Ohio, another Midwestern state, on Monday. Polls there show Trump with a slight edge; no Republican has ever won the presidency without winning the state, where there are both large industrial centers and vast farmlands.

FILE - then-New York mayoral candidate Anthony We
FILE - Then-New York mayoral candidate Anthony Weiner speaks during a news conference alongside his wife Huma Abedin in New York.

Several polling analysts say Clinton is close already to securing the 270 electoral votes or even above that majority figure.

One of the closest of the battleground states is Florida, in the southeastern part of the country. Both Trump, who has an oceanfront mansion as a second home in the state, and Clinton have held numerous rallies in Florida, hoping to gain a last-minute edge in a state with 29 electoral votes. She campaigned Sunday in Florida, and she is making three more stops there on Tuesday.

Numerous Democrats have attacked Comey for divulging the existence of the renewed email probe so close to the election.