Vice presidential picks have traditionally taken on the role of political attack dog, laying into opponents so that their running mate can appear above the political fray. That's generally been less true since former President Donald Trump scrambled political norms.

But Walz, the Democratic governor of Minnesota, made it to national prominence by labeling rival Republicans "weird." Vance, the Republican junior senator from Ohio, has torn into Vice President Kamala Harris ' party on immigration, notably by spreading a false story about Haitian immigrants in his home state that Trump then cited during his own debate with Harris.

Here's a look at past vice presidential debates -- and the larger role of the office Walz and Vance are both seeking.

What is the vice president's job?

The vice president presides over the Senate and is empowered to break ties, as Harris has done a record 33 times. She exceeded the previous high mark last year, which had held since John C. Calhoun was vice president from 1825 to 1832. The officeholder also presides ceremonially in Congress over the certification of electoral results, which Vice President Mike Pence did even after a mob of Trump supporters stormed the U.S. Capitol on Jan. 6, 2021, in a bid to halt the process and transition of power, with some chanting, "Hang Mike Pence!"

But the vice president's main job is to be ready to take over if something happens to the president. Nine have done so following a president's death or departure from office -- the last being Gerald Ford, who became president when Richard Nixon resigned in 1974.

The Constitution's 25th Amendment, ratified in 1967, spelled out the succession rules, stating that the vice president becomes president "in case of the removal of the president from office or of his death or resignation." It also allowed the president and Congress to nominate and approve a new vice president if that office is vacated.

Vice presidential historian Joel K. Goldstein said two recent assassination attempts against Trump raise "the saliency of succession." But he added that many voters view vice presidential nominees as appendages of the candidates who selected them, not necessarily as potential future presidents themselves.

"People do look at somebody as, are they ready to be a heartbeat away?" Goldstein said. "But it is also a question of how good a decisionmaker is the person who chose them."

Memorable vice presidential debates featured Palin, Bentsen -- and Harris

In 1992, Adm. James Stockdale, running mate of third-party candidate Ross Perot, was going for breezy but seemed befuddled when he opened the debate by saying, "Who am I? Why am I here?" His later response to a question, "I didn't have my hearing aid turned up," only reinforced that perception.

The debate between No. 2s was highly anticipated in 2008 after Republican Arizona Sen. John McCain selected Alaska Gov. Sarah Palin as his running mate and saw a bump in the polls. But her showdown with then-Delaware Sen. Joe Biden is best remembered for Palin approaching him before the start and saying, "Can I call you Joe?" That was Palin attempting to keep from mistakenly calling her opponent "O'Biden," conflating Biden's name with that of his running mate, then-Illinois Sen. Barack Obama.

The vice presidential nominee and Texas Democratic senator, Lloyd Bentsen, offered a stinging rejoinder against his opponent, Republican Sen. Dan Quayle of Indiana, in 1988. After Quayle compared himself to John F. Kennedy, Bentsen replied, "You're no Jack Kennedy, senator." But it was one of the Democratic ticket's few high points in a race it lost handily.

In 2020, Harris faced off with Republican Vice President Mike Pence and declared when he tried to interrupt her, "I'm speaking," a line she's reprised in this campaign. But both candidates might have been overshadowed by a fly that perched on Pence's hair for what felt like an eternity.

Will the debate affect the campaign?

A nominee's choice of No. 2 has historically made little Election Day difference. This year could be different.

Historical analysis by Mark P. Jones, a political science professor at Rice University in Houston, suggests that voters aren't really swayed by a candidate's running mate. Even the idea of using a pick to balance a ticket -- like pairing the first major party nominee who is a woman of color with a white male in the case of Harris selecting Walz -- may also be overstated.

"The evidence we have is that they're really voting for the presidential nominee," Jones said of Americans through the decades.

A key caveat might be that, given just how close the current race is looking to be in swing states, "It's always possible that, at the margins, it may matter," Jones said.

One reason why the Walz-Vance debate might shift more opinions this year is that Harris and Trump shared a stage only once, in early September. That means Tuesday may be the last chance before Election Day for voters to see the two tickets square off directly.

But, more likely, both Walz and Vance will simply need to avoid memorable unforced errors that can be endlessly replayed. Jones said such a race-shifting gaffe is unlikely -- but not impossible.

"They're disciplined," Jones said. "But all it takes is one."