The public relations disaster that former Secretary of State Hillary Rodham Clinton suffered in March registered in a poll Tuesday, with possible Republican candidates surging ahead of her as voters doubt her honesty in key presidential swing states.
Mrs. Clinton lost ground in hypothetical matchups against every potential Republican rival in the bellwether states of Florida, Ohio and Pennsylvania in the wake of an email scandal and other controversies that erupted last month, Quinnipiac University’s Swing State Poll found.
The closest contests are in Florida, where former Gov. Jeb Bush tops Mrs. Clinton 45 percent to 42 percent, and in Pennsylvania, where Sen. Rand Paul of Kentucky narrowly beats her 45 percent to 44 percent, according to the poll.
Mrs. Clinton had the lead in both matchups in the same poll Feb. 2.
In Ohio, Mrs. Clinton topped Mr. Paul 46 percent to 41 percent. That is a significant tightening of the race since the February poll, when Mrs. Clinton had a 12-point advantage over Mr. Paul, 48 percent to 36 percent.
The former secretary of state, senator and first lady still beats every Republican in the Buckeye State, though by smaller margins than in February.
Mrs. Clinton also has lost the double-digit leads she once held over most Republicans in all three states. Her only double-digit leads now are in Ohio over Sen. Ted Cruz of Texas, 48 percent to 38 percent, and Wisconsin Gov. Scott Walker, 49 percent to 38 percent.
Mrs. Clinton, the undisputed front-runner for the Democratic presidential nomination, remains the strongest candidate with the best overall poll numbers of any Democrat or Republican. However, her favorability rating took a hit in each state.
In Pennsylvania, voters split 48 percent to 47 percent on Mrs. Clinton’s favorability, a steep drop from the 55 percent to 38 percent margin in February.
The poll also showed that voters don’t trust her now.
Florida voters said Mrs. Clinton is not honest and trustworthy, by a margin of 50 percent to 41 percent. Pennsylvania voters questioned her integrity 49 percent to 44 percent, and voters in Ohio who said they didn’t trust her was 47 percent compared with 46 percent who did.
The erosion of trust stems from revelations in early March that Mrs. Clinton exclusively used a personal email account for official business while secretary of state, a practice that might have violated federal open-record laws and shielded her communications from Congress and from public inquiries under the Freedom of Information Act.
Mrs. Clinton said it was more convenient for her to mingle personal and official email in a single account.
“Something for Secretary Clinton’s team to worry about [is] 36 percent of independent voters in the key state of Ohio say they are less likely to vote for her because of the email controversy,” said Peter A. Brown, assistant director of the Quinnipiac Poll.
“Majorities in each state think Clinton still has questions to answer about her emails,” said Mr. Brown. “Voters in each state are evenly divided on whether congressional hearings are warranted, although a majority thinks such a hearing would be politically motivated rather than justified.”
Mrs. Clinton also was rocked in March by a federal cronyism scandal that involved her brother, Anthony Rodham, and two of her close political allies, Virginia Gov. Terry McAuliffe and former Pennsylvania Gov. Edward G. Rendell.
An earlier disclosure that the Clinton Foundation pocketed foreign donations while she was secretary of state raised concerns about conflicts of interest.
Despite the drop in favorability, Mrs. Clinton does better on that measure than Republican contenders, except for Mr. Bush and Sen. Marco Rubio in their home state of Florida.
“The good news for Hillary Clinton is that the email controversy has not done huge violence to her presidential chances. But the matter is taking a toll on the former secretary of state’s public image,” Mr. Brown said.
He noted that voters still consider Mrs. Clinton a strong leader, a key characteristic for a presidential candidate. Voters see Mrs. Clinton as a stronger leader than her lesser-known potential Republican opponents.
The Swing State Poll focuses on Florida, Ohio and Pennsylvania because no candidate since 1960 has won the presidential election without winning at least two of these three states.