But they also flagged warning signs. A majority said her campaign had so far left them, and party activists, flat. Her message, they said, has been too generic, tethered to well-worn talking points such as raising the minimum wage and "fighting for the middle class."
They questioned the return on her spending: McGinty burned through $7 of every $10 raised last quarter without any gains in polling. Her campaign is now counting on outside support for a TV push over the finish line.
And finally, while asking not to be named critiquing their potential nominee, they worried about her embrace of insider endorsements - Gov. Wolf and former Gov. Ed Rendell, big labor unions, and top Senate Democrats - in a year when voters have spurned traditional politics.
"People were expecting Katie to have a bigger impact than she has so far," said David Dunphy, a Democratic consultant based in Philadelphia, one of the few willing to speak publicly.
But he, like the others, said McGinty has time to rally, because none of her rivals has broken away from the pack and the contest has yet to be fully engaged. On Friday night, she'll share a stage in Hershey at a candidate forum with her two main competitors: former Rep. Joe Sestak and Braddock Mayor John Fetterman.
Despite multiple requests, McGinty was not available for an interview Wednesday or Thursday.
A spokeswoman said McGinty has kept a busy schedule of party events, meetings, media hits, and diner tour stops, even if many are not widely publicized.
"Soon, all of Pennsylvania will know what our 10,000 grassroots supporters already do: Katie is the best candidate to take on Pat Toomey," said spokeswoman Sabrina Singh.
For some Democrats, getting to know McGinty - a onetime gubernatorial candidate who spent about six months as Wolf's first chief of staff - is part of the problem.
In late January, as she was meeting with Democratic senators in Washington, her chief rival, Sestak, was in her home county, Chester, winning the local party endorsement.
Brian McGinnis, who had worked on Sestak's campaigns years ago and now chairs the Chester County Democrats, said McGinty could be a "great candidate" but needed to be more visible.
"I'm really not sure what her campaign has been about so far," he said.
A Franklin and Marshall College Poll released last week showed McGinty with 12 percent support among Democratic primary voters - statistically unchanged from the 13 percent she had when she entered the race in August.
Sestak, a former admiral from Delaware County, had 21 percent support, and Fetterman had 8, both up a handful of percentage points since October.
Joseph Vodvarka, a late entrant to the race, was not included.
The poll suggests no candidate has reached many voters, but during his time in the House and his Senate run in 2010, Sestak built a record of winning grassroots support. Fetterman has generated outsize media attention with his unvarnished persona, despite lagging badly in funding.
Even McGinty's critics caution that it is too early to draw conclusions. So many voters remain undecided on the Senate contest that any candidate who mounts a sustained run on television could grab hold of the race, they said.
And most did not expect serious movement in the polls for a few weeks, at least - Sestak, for example, rallied to win his 2010 primary with a TV barrage in the campaign's final four weeks.
"This is a wide-open race," said Franklin and Marshall pollster G. Terry Madonna. "They're all basically unknown."
He chalked up Sestak's polling edge to residual name recognition from his 2010 run, and said the contest would take shape once ads go up - the most reliable way to reach voters in such a large state.
"Nobody's put any financial resources into communicating their message," said Democratic consultant Mark Nevins, leaving so many voters undecided that "the difference between first place and third place is more or less irrelevant."
And many said the coming weeks would be more revealing: Voters and donors have been focused on the presidential contest, drowning out the Senate candidates.
McGinty supporters argue she will surge once people hear her story: daughter of a Philadelphia police officer and a restaurant hostess who rose to become a top environmental official in the Clinton White House and Rendell administration, and Wolf's chief of staff.
Her attempt to become Pennsylvania's first female senator could also dovetail with a Hillary Clinton campaign.
McGinty allies argued that the pressure was on Sestak.
"The fact that the previous nominee doesn't have a huge, almost insurmountable, lead is the story," said T.J. Rooney, who chaired McGinty's run for governor in 2014.
Sestak's camp said he was focused on voters, not polls.
Sestak will also likely have more money for the air war. He had a $1.4 million cash advantage as of the latest campaign filings.
McGinty is working furiously to close that gap, but Rendell said it would also take a burst of spending from outside political groups - though, by law, they cannot formally coordinate.
A spokeswoman for EMILY's List, the Washington-based group that backs Democratic women and that is one of McGinty's prime supporters, said she could not comment on potential ad buys, but called the Pennsylvania race "a top priority."
Unless McGinty and the organizations supporting her can buy from $3.5 million to $4 million of television time, "she won't win," said Rendell, her campaign chairman.
If they do hit that mark, he said, "I think she will win."