Pennsylvania Republicans have a couple of choices this year when it comes time for them to select their nominee for governor: a slumlord and deadbeat dad, or a phony and a disgrace.

That's according to the characterizations the two leading candidates, businessman Paul Mango (the accused phony) and state Sen. Scott Wagner (the supposed slumlord), have offered about one another. Val DiGiorgio, who chairs the state GOP, has pleaded with the candidates to stick to the issues, saying "personal attacks like this hurt our democratic process."

But personal attacks have become all too common this year. Even though it's still early in the campaign season, politicians around the country are attacking each other with gusto, lobbing insults that are often personal in nature. "Negativity is as old as elections," says David Redlawsk, who chairs the political science department at the University of Delaware, "but the nastiness we're seeing today is different. It is more personal, more slash and burn."

Redlawsk is coauthor of the book The Positive Case for Negative Campaigning, which argues that attacks on opponents can offer voters information about a politician's record that can help them make informed choices. "Candidates, particularly challengers, have to paint their opponents in a way that will convince voters not to vote for them," he says. "That comparison is always going to be: the other's guy's no good; I'm good."

Case in point: Ohio Lt. Gov Mary Taylor released an ad that seeks to tar Attorney General Mike DeWine, her gubernatorial opponent, for voting with Hillary Clinton in the U.S. Senate 962 times.

Outside groups tend to be harsher than candidates themselves. Back in February, a group called People for a Progressive Florida went after Democrat Javier Fernandez through emails, texts and robocalls that purported to feature Fernandez himself confessing to lobbying for casinos and retail sex toy shops. Fernandez is the Democratic nominee in Tuesday's special state House election in Florida.

And a recent press release from the Democratic Governors Association went after Tim Pawlenty, the former GOP governor of Minnesota and once again candidate for the office, proclaiming: "Tim Pawlenty headlines hate group dinner to discuss his homophobic record."

What's different in 2018, though, is the willingness of candidates to hurl insults directly at their opponent, targeting not their records but their personality traits. "You do not want a liar as the governor of the state of Illinois," Chris Kennedy said at a candidate forum in Illinois, describing J.B. Pritzker, who ultimately won the Democratic nomination for governor.

"We've sort of hit the bottom of the rung," says Martin Medhurst, a professor of political science and rhetoric at Baylor University. "Or at least I hope it's the bottom."

There are a number of reasons why attacks are becoming malicious. Negative partisanship -- the belief that however bad the politicians are in your own party, the ones on the other side are far worse -- is a dominant strain in contemporary politics. The willingness of politicians to call each other Nazis or the Antichrist is an outgrowth of the sense that victory by the other side could bring about existential ruin.

Certainly, social media plays a role. Stinging political attacks can travel faster and farther than they used to.

Take the comments directed at the students who survived the mass shooting at Stoneman Douglas High School in Parkland, Fla., and emerged as gun control advocates. Leslie Gibson, who was running for the state House in Maine, dropped out after calling Emma Gonzalez on Twitter a "skinhead lesbian" and David Hogg a "moron" and a "baldfaced liar." The Fraternal Order of Police pulled its endorsement of Julie Killian, the Republican candidate in a high-profile special state Senate election in New York, after one of her fundraisers tweeted insults at Hogg. And Stephan Miller, a contributor to the Fox News Channel's website, tweeted above a picture of Hogg at Saturday's White House Correspondents Dinner: "He looks tall standing on top of that pile of bodies."

Then there's President Trump. Both as candidate and president, Trump has repeatedly hurled insults at politicians and public figures who have challenged him. Trump didn't lower the tone of political discourse by himself, Redlawsk notes, but his example has certainly had an influence. "It's one thing to be a candidate who attacks," Redlawsk says. "It's another thing to be the president of the United States and be in this mode of constantly tearing down anyone who opposes you."

Trump's supporters sometimes bemoan his hate-tweeting, but many like the fact that he's willing to give at least as good as he gets. "The base has been longing for years for somebody who punches back," conservative commentator and author Mark Steyn said on Fox News on Sunday.

Hitting hard seems to be fair play. That was the reaction of liberals to the outcry over comedian Michelle Wolf's performance at the White House Correspondents Dinner.

Conservatives and some journalists complained Wolf had crossed a line with attacks on White House Press Secretary Sarah Huckabee Sanders, among others. But lots of liberals defended Wolf, saying that Trump set the tone by so readily mocking people for their looks or even disabilities. "Dear Republicans-Thanks for your fake outrage with Michelle Wolf," tweeted Scott Dworkin, cofounder of The Democratic Coalition, an anti-Trump group. "You opened the door for us to remind everyone of every single raunchy and disgusting thing Trump’s ever said."

Dear Republicans-Thanks for your fake outrage with Michelle Wolf. You opened the door for us to remind everyone of every single raunchy and disgusting thing Trump’s ever said. Which is much worse—by a bigger landslide than his popular vote loss. He’s the president not a comedian.

— Scott Dworkin (@funder) April 30, 2018 Jim Geraghty, a political reporter for National Review, called for more even-tempered discourse on Twitter, suggesting that either "everything is fair game" on both sides or "decorum, decency respect are required."

"She said obnoxious things," Geraghty wrote of Wolf. "Yes, the president says and tweets obnoxious things. Citing one to justify the other in either direction is an ipso facto defense of obnoxiousness."

But it can be useful in politics to be obnoxious. Not every attack works, Medhurst says, but "to the extent they're effective, you're going to see more and more of them."

Redlawsk compares the logic of personal attacks to the nuclear arms race during the Cold War and the era's doctrine of mutually assured destruction. No one wants to disarm unilaterally, and so the attacks ramp up. "What do you do when you're a subject of attack?" he asks. "Game theory argues that you can't sit back and take it, so you might as well go on the offensive to begin with."