Republican incumbent Sen. Ron Johnson and his Democratic challenger, Lt. Gov. Mandela Barnes, duked it out at their first debate at the PBS studios in Milwaukee on Friday.

The duo addressed topics that have cast a shadow on their campaigns, with Sen. Johnson responding to past comments on Social Security, which he’s proposed to make discretionary rather than mandatory spending -- a move Democrats say puts the program in jeopardy.

"I want to make myself very clear, I want to save Social Security. I want to to save Medicare," said Johnson.

Barnes responded that Social Security should be strengthened and that the "wealthy should pay for their fair share," adding that Johnson had once called the federal benefit program a "Ponzi scheme."

The Democratic nominee was also given the opportunity to discuss his stance on bail reform, an issue that Republicans have focused on in their many crime-related attack ads against Barnes.

"I appreciate the question because it has been sensationalized and it's also been mischaracterized," said Barnes. "I support bail reform."

Johnson rebutted that Wisconsin has a problem with "skyrocketing crime" and pointed at Barnes' past record that he wrote a bill that would eliminate cash bail.

"First of all you have to fully fund the police and of course my opponent is opposed to fully funding police budgets," said Johnson.

The two also clashed over Jan. 6, 2021, as Barnes said Johnson "left behind" the 140 officers at the insurrection -- a jab at Johnson's comments earlier this week calling the mob violence that day "not an armed insurrection" and that the protesters "did teach us" how to use flag poles as weapons.

Johnson on Friday said Vice President Mike Pence did the “right thing” by certifying Joe Biden’s win, and used mentions of Jan. 6 to discuss protests that occurred in the summer of 2020: "If you want to talk about rioting, we should take a look at what happened in Kenosha.”

- ABC News’ Paulina Tam

President Joe Biden was focused on his midterm messaging In Hagerstown, Maryland on Friday, while criticizing GOP lawmakers for requesting Democratic-led infrastructure funding that they publicly opposed.

Biden highlighted a CNN report that detailed some GOP members of Congress who voted against the Bipartisan Infrastructure Law and called it “socialism,” but are now asking for funds to help their districts. The president even name-checked several of them and what they’ve requested, like Republican Rep. Paul Gosar of Arizona and Republican Sen. Rand Paul of Kentucky.

“Socialism. I didn’t know there were that many socialist Republicans. I was surprised to see so many socialists in the Republican caucus," he said.

The president spent much of his speech touting his legislative wins and benefits that stem from the American Rescue Plan, Bipartisan Infrastructure Law and the Inflation Reduction Act. He warned what could happen if Congress flips after the midterms.

“If Republicans take control of the Congress, the $2,000 cap on prescription drug costs we just passed goes away. Gone. If they take back control of the Congress the $35 month cap on insulin for folks on Medicare we just passed goes away,” he said, again calling out specific GOP members and what their involvement might be in challenging the landmark policies.

“And folks, it's not just the Inflation Reduction Act, they’re coming after your Social Security and Medicare as well,” Biden said.

“There's a senator from Wisconsin, Ron Johnson... As he says, Social Security and Medicare should be on the chopping block every single year.”

–ABC News’ Justin Gomez

Candidate debates proved hard to come by this midterm cycle, with resistance mostly from Republican candidates who said they wished to debate on their own terms.

Some Democrats in key swing states have refused to face opponents who espouse the false election claims. Voters in Arizona, North Carolina and Wisconsin, the pivotal battleground races, are able to see their Senate candidates face off for the first and probably only time this week.

Arizona’s matchup between incumbent Sen. Mark Kelly and Republican challenger Blake Masters kicked off the string of debates last night with some memorable moments.

Kelly voiced that he could stand up to President Joe Biden and his own party, particularly on border security. "I’ve spent a lot of time on our southern border, and let me just say it’s a mess. It’s a chaos. It’s crisis after crisis," Kelly said.

Next up is North Carolina and Wisconsin. Former state chief justice and Democratic candidate Cheri Beasley will meet GOP candidate Rep. Ted Budd on stage in Raleigh at 8 p.m. ET on Friday, while incumbent Republican Ron Johnson is facing off against the state's Lt. Gov. Mandela Barnes in Milwaukee at 8 p.m. ET.

–ABC News’ Libby Cathey, Paulina Tam and Hannah Demissie

The drama has been back East: a colorful matchup in Pennsylvania between two outsized personalities, an ambitious Florida governor who hosted the president this week and a political storm in Georgia is testing trust and loyalties surrounding the GOP Senate candidates.

But those states might not matter nearly as much depending on what happens out West. Senate and gubernatorial races in Arizona and Nevada -- and perhaps a Senate campaign in Colorado as well -- are no longer being overlooked and could be where majorities are won or lost, with the stakes even higher going into 2024.

Issues surrounding the southern border and inflation are particularly resonant and intense in those states, and conspiracy theories around the last election have flourished inside the state GOPs. New polling from CNN confirms concerns that have been growing among Democrats -- and optimism that's been growing among Republicans.

Nevada Sen. Catherine Cortez Masto is in a virtual tie with her Republican opponent, Adam Laxalt, trailing 46%-48%, while Arizona Sen. Mark Kelly is leading Republican Blake Masters 51%-46%, according to the CNN survey. Kelly and Masters faced off for their first and most likely only debate of the election cycle on Thursday night.

See more here.

–ABC News’ Rick Klein

Senator Elizabeth Warren, D-Mass., is expected to campaign on Oct. 26 for Wisconsin Gov. Tony Evers, Lt. Gov. Mandela Barnes and state Attorney General Josh Kaul in what is the latest appearance by a prominent Democrat to rally voters weeks before the high-stakes midterms.

The events with Warren, first reported by ABC News, will also feature Wisconsin's Democratic senator, Tammy Baldwin.

Baldwin, Evers, Kaul and Warren will host an early voting event focused on young people near the campus of the University of Wisconsin at Madison, according to the Wisconsin Democratic Party.

Baldwin and Kaul are expected to walk with a group of students to an early voting location to cast their ballots.

Barnes is in a tight race to defeat incumbent Sen. Ron Johnson, a Republican.

Polling shows that Evers is in a toss-up race, too, against Republican challenger Tim Michels, with the latest FiveThirtyEight average showing Evers with less than 1% lead.

In a statement to ABC News, the Wisconsin Democratic Party Chair Ben Wikler said: "This election is deadlocked, and no one can sit this out. If Wisconsin students turn out to show the GOP they won’t let them trample on their rights, Democrats will win up and down the ballot. Senator Warren is an electrifying voice who will bring her incomparable energy and vision to mobilize Wisconsin students at exactly the moment it’s needed most."

In her own statement, Warren said, "Voters in Wisconsin know what is at stake in this election. Wisconsinites have the opportunity to vote for [Senate nominee] Mandela Barnes, Tony Evers, and Democrats all the way down the ballot who will fight to restore a woman’s right to choose, to bring down costs, to build an economy that works for all of us, and to attack the climate crisis head on. I’m proud to join them in this critical fight."

Warren joins a growing list of big-name Democrats -- including former President Barack Obama -- to hit the trail in various battleground states before Election Day.

They hope to counter the history of rough midterm elections for the party in power, plus major headwinds like high inflation, in part by focusing on Republican-backed restrictions on abortion and the extremism of some of the GOP nominees.

When asked by reporters after a gubernatorial debate on Friday whether former President Donald Trump planned to stump for the Republican ticket in Wisconsin, Brian Fraley, a communications specialist for the Michels campaign, said they would notify the press if such an event was scheduled.

Fraley said then that Obama coming to Milwaukee was a "sign" that the Evers campaign was "in trouble" because "they're calling in all the big dogs."

-- ABC News' Cheyenne Haslett and Paulina Tam