WASHINGTON » Richard Nixon is back.

The ghost of the 37th president hovers over Democrat Hillary Clinton and Republican Donald Trump. Both presidential campaigns use the president who resigned in disgrace over the Watergate scandal in 1974 as the gold standard to show how crooked and dishonest the other is.

Yet both candidates also seem to have a little of the notoriously thin-skinned, conspiratorial, and vengeful Nixon in them, presidential historians say, from Trump embracing the “law and order” theme that catapulted Nixon to the White House in 1968 to their utter disdain for the press to political controversies spawned from technology — Nixon’s secret Oval Office tape recorder and Clinton’s private home email server.

“The shadow of Nixon hangs over the campaign,” said David Gergen, who worked under Nixon and former President Bill Clinton. “It’s remarkable how many times we’ve gone back to Nixon to make comparisons over the last few months.”

Just Wednesday, Trump conjured up Nixon anew, saying that Hillary Clinton’s email controversy “is like Watergate, only it’s worse because here our foreign enemies were in a position to hack our most sensitive national security secrets.”

Democratic vice presidential candidate Tim Kaine referenced Nixon last Sunday by comparing the cyber hack of the Democratic National Committee to the Watergate break-in and blasting Trump for seemingly encouraging Russia to engage in cyber espionage to unearth some of Clinton’s missing emails.

Nixon “had to resign over an attack on the DNC during a presidential election,” Kaine said on ABC. “This is serious business.”

Trump’s campaign has borrowed liberally from Nixon in terms of policy and personnel. Nixon disciples such as Roger Stone and recently ousted Fox News Chairman Roger Ailes frequently speak with Trump. Ailes is reportedly helping Trump prepare for debates against Clinton.

Trump also used Nixon’s 1968 Republican National Convention acceptance speech in Miami as inspiration for the 2016 candidate’s convention acceptance address in Cleveland in July, according to former Trump campaign chairman Paul Manafort.

And Nixon’s law and order message to an America reeling from the Vietnam War, anti-war protests on college campuses, crime and racial unrest in cities in the late 1960s is “pretty much on line with a lot of the issues that are going on today,” Manafort told reporters at a convention breakfast hosted by Bloomberg.

Nixon’s victory over Vice President Hubert Humphrey in 1968 marked a comeback for a figure who’d earned a reputation as a hard-edge, sometimes unscrupulous, politician and the unflattering nickname of “Tricky Dick” for his unapologetic style.

After losing the presidential election to John F. Kennedy in 1960, Nixon re-emerged as the “New Nixon” in 1968, softening the sharp elbows he’d wielded as a hard-charging member of the Communist-seeking House Committee on Un-American Activities in the 1940s and a U.S. senator and Dwight Eisenhower’s vice president in the 1950s. He ran as an empathetic candidate yet one who would stand up to lawbreakers.

But once in the White House, parts of the old Nixon resurfaced. He had a vindictive streak toward Washington elites, certain elected officials, journalists and others who he thought were out to get him.

He maintained an enemies list and tried to use the FBI and Internal Revenue Service to investigate those who he felt had wronged him.

Both Trump and Clinton channel some of Nixon’s mean streak, especially when it comes to the press, said Robert Watson, the editor of the “American Presidents” and “American First Ladies” books.

Angry over what he considers unfairly negative coverage, Trump banned some reporters and media outlets from his campaign events. He lifted the ban last week.

As president, he said he would “open up” libel laws to make it easier to sue reporters.

Clinton has shown her dislike for the press by not conducting a news conference in more than 270 days before finally taking questions last week aboard her new campaign plane.

“Hillary’s disdain and her lack of access to press is even beyond Nixon,” Watson said. “But I would say Trump is unprecedented in American history. We have never seen a candidate flat-out making a blacklist of media outlets and reporters he will not talk to. We have never had a major-party candidate simply censor the media and threaten the media. This even goes beyond Nixon.”

Clinton shares another problematic trait with Nixon: trust issues. A recent CNN poll found that only 35 percent of voters consider her honest and trustworthy vs. 50 percent for Trump.

“I think it’s unfair to call her Nixonian, but there are some traits that are similar: secretiveness, being a little careful with the truth,” Gergen said. “Trump has done better than anyone would have expected in making the charges stick that she is somehow unethical.”

She could turn that around by adopting another Nixonian trait — reinvention, suggested Gil Troy, a history professor at Montreal’s McGill University.

“Nixon reintroduced himself in 1968 as older, wiser, even-tempered,” said Troy, the author of “The Age of Clinton: America in the 1990s.” “He was well-known in politics and hated, but he was able to reinvent himself and reassure people on the trust issue just enough.”

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©2016 McClatchy Washington Bureau