PHILADELPHIA – Bernie Sanders and Elizabeth Warren, two progressive senators who are among the most popular and well-regarded figures in the Democratic Party, are making their much-anticipated debuts on the campaign trail for Senate candidates by stumping for Katie McGinty, who is challenging incumbent Pat Toomey in Pennsylvania.

The appearance of the two most popular Democratic figures outside of President Obama and Vice President Biden is a sign of how critical Pennsylvania will be in determining which party controls the Senate in 2017. But it’s also a sign that of all the Democrats challenging incumbent GOP senators this year, McGinty might need the most help.

In some of the most competitive races this cycle, Democrats recruited candidates who were well known in their states and had won elections there, from Gov. Maggie Hassan in New Hampshire to former Gov. Ted Strickland in Ohio to former Sen. Russ Feingold in Wisconsin. In Nevada, former Attorney General Catherine Cortez Masto was elected twice statewide, and Missouri Secretary of State Jason Kander won statewide in 2012. In Florida, North Carolina and Arizona, the Democratic candidates have never won statewide, but have served either in Congress or their state legislatures.

But McGinty, the chief of staff to Pennsylvania Gov. Tom Wolf and a former Clinton administration official, has never held elected office – her only previous run resulted in a third-place finish in the Democratic primary for governor in 2014. She’s leading Toomey in the polls by just two-tenths of a percentage point, according to the RealClearPolitics average, but she’s being outpaced in the state by Hillary Clinton, who’s beating Donald Trump by 6.2 percentage points.

Much of that is due to McGinty’s lack of name recognition across the Keystone State. In a recent Monmouth University poll, McGinty was viewed favorably by 27 percent of likely voters and unfavorably by 17 percent, but 56 percent had no opinion of her. Even worse, 61 percent of independents had no opinion, and she was losing them to Toomey by 12 points. Her Republican rival was viewed favorably by 32 percent, unfavorably by 30 percent, with 38 percent holding no opinion.

There are positives for both candidates to cling to. Pennsylvania has gone Democratic in every presidential race since 1988 but in three of those presidential years, the state also elected Republican senators. Still, the state has nearly a million more registered Democrats than Republicans, giving McGinty a bigger pool of voters in her base.

But even reliable Democrats don’t know her well yet. She has an overwhelmingly positive image among party members, according to Monmouth, with 50 percent viewing her favorably and just 2 percent unfavorably. But 49 percent of Democrats in the poll had no opinion of their party’s candidate for Senate.

That’s why Warren and Sanders are such effective, and necessary, surrogates here. Warren visited her Friday in the Democratic hub of Philadelphia, joining McGinty at a rally on the campus of the University of Pennsylvania, which drew a packed auditorium of several hundred people. Warren’s status as a progressive icon means there weren’t many swing voters in the audience – it was an event designed specifically to ignite the base. This Friday, Sanders will join McGinty at Carnegie Mellon University in Pittsburgh.

“When Warren and Sanders and other high-profile surrogates come to town is absolutely a benefit to the McGinty campaign to be able to get those clips of the two, of Warren and McGinty campaigning together on the evening news in Philadelphia and Sanders and McGinty in Pittsburgh,” said Martha McKenna, a former political director at the Democratic Senatorial Campaign Committee. “It’s hard to do on a regular basis and it’s a real benefit.”

Philadelphia and Pittsburgh are crucial areas for Democrats in Pennsylvania, as they’re much bluer than the rest of the state. Democrats typically need to drive up massive victories in the urban areas to outpace Republican support in the rest of the state.

Those efforts are particularly important against Toomey, who has been making a concerted effort to reach independents, swing voters and ticket splitters who won’t support Trump. Toomey, who has spent much of his campaign discussing security issues like sanctuary cities and law and order, has spent the last several weeks talking about middle-class taxes and touting his record on gun control. He’s been endorsed by two gun-control groups, and one, a PAC led by former New York City Mayor Mike Bloomberg, is advertising heavily on his behalf, which could help swing moderate voters to his side.

Warren tried to blunt that with her message during the rally here Friday. She extensively tied Toomey to Trump and criticized the Republican senator for his indecision on whether to back the GOP nominee – Toomey has said he is still “watching and listening” before making a decision.

Warren brought up a list of Trump’s biggest controversies, including his attacks on the Mexican heritage of the judge overseeing a case against Trump University; his illegal political contributions to the Florida attorney general who was investigating Trump University but ultimately dropped the case (Trump’s campaign has said the donation was a “clerical mistake”); his calling illegal immigrants “rapists and murderers”; and some of his offensive remarks about women.

“Where has your big brave senator Pat Toomey been?” Warren asked the crowd. “He’s trying to hide out. He’s trying to duck and weave. But despite everything that Donald Trump says, Pat Toomey still won’t say that he won’t vote for him."

Toomey’s campaign sent out a fundraising email to supporters the morning after Warren’s visit asking for donations to “help Pat fight back,” saying, “Now that the far-left liberals’ favorite Senator is publicly campaigning for Katie McGinty, she’ll have the attention and support of even more left-wing Democrats across the nation.”

Ted Kwong, a spokesman for Toomey, said Sunday that "there's a reason why Elizabeth Warren and Bernie Sanders win elections in Massachusetts and Vermont, and not in Pennsylvania. We're not liberal extremists here. Katie McGinty will find that out on Election Day."

Warren and McGinty also made an appeal to the historic nature of her candidacy: Pennsylvania has never elected a female senator or governor. In talking about some of her most important issues in the Senate, Warren repeatedly tied McGinty to herself and Clinton, using the refrain, “Katie, Hillary and I will be fighting for it” when talking about Wall Street reform, combating climate change and a host of other issues.

McGinty also acknowledged the historic nature of her candidacy. She mentioned that Clinton could be the first “Madame President” and said, “I’d appreciate it if we thought about doing a two-for-one. When we are shattering that White House glass ceiling, will you join me in shattering that Senate glass ceiling as well?”

Multiple voters at the rally who spoke with RealClearPolitics admitted they didn’t know much about McGinty, and several said they were there mostly to see Warren – though all of them said they already planned to vote for McGinty in November.

Patrick Keough, 23, moved to Philadelphia from Massachusetts within the last year and registered to vote at a Clinton rally over the summer. He said he plans to vote for McGinty because she’s pro-choice and has a good economic message, but admitted he didn’t know much about her beyond that.

“Honestly, just what I’ve seen on commercials and I read her Wikipedia page,” Keough told RCP. “I’ve been trying to educate myself on Pennsylvania politics since I’m registered to vote here. I heard about her peripherally at the Hillary rally, but other than that” he doesn’t know many specifics.

Zoe Braccia, 18, a freshman at Penn and a first-time voter, was wearing a Hillary Clinton hat and said she’s a strong supporter of the former secretary of state. She also didn’t know much about McGinty or Toomey, but said she planned to vote for the Democrat because she holds the same values as Clinton.

John Ash, 46, a steelworker from Philadelphia who has campaigned for McGinty on behalf of the steelworkers union by handing out leaflets both during the primary and general election, said Warren provided a big boost. He pointed out that McGinty was down 10 points in the weeks leading up to the April primary, but won that election by double digits after boosting her name ID. He said a similar thing would happen in the general election, except that instead of trailing Toomey, she’s now winning by a slim margin.

“I just think Katie is the right person for the job,” Ash said. “Not that I’m that dead-set against Toomey, but I think Katie can do a better job for the workers here in Philadelphia, and I think she’s going to stand more for the American workers than Toomey did."

Barbara Mail, 64, a retired teacher from Philadelphia, pointed out the obvious: Most of the people at the rally were already inclined to support McGinty. She said she wished Warren’s visit could have reached a wider audience, but added that it was important to galvanize the base. After the event, she signed up to volunteer for the campaign, something she has never done before. She said she isn’t excited about the task, but “you have to walk the walk, you can’t just talk the talk."

“I think most of these people already knew that they wanted to oust Pat Toomey, but I don’t think it hurts because a lot of these people are energized to go out and help,” Mail said after the event. “That’s what we need really, to get out the vote.”