McGrath is the favorite of the Senate Democrats’ campaign arm and many sitting senators, and it’s hard to imagine she could lose a primary in which she’s outspent her opponents combined by a nearly 30-1 margin through early June. But there are signs it's turning into a real race: Booker is panning McGrath as a bland national Democrat who is predictably tacking to the center, while McGrath is biting back at Booker, accusing him of talking a big game on health care and voting rights but not backing it up.

"I don't really know what position Amy McGrath takes because she goes back and forth on everything depending on what consultants seem to say,” Booker said in an interview. “I know that Kentuckians can smell BS from miles away.”

“I’m not, as Mr. Booker claims, 'a pro-Trump Democrat.' I’m pro-Kentucky and pro-America,” McGrath said, refuting her top opponent in a POLITICO interview after months of keeping her fire trained on McConnell.

McGrath's position as McConnell's leading challenger and the then-viral advertising for her failed 2018 House bid have made her a darling of Democratic small donors. As of early June, she had a staggering $19 million in cash on hand, more than McConnell's 2014 opponent, then-Secretary of State Alison Lundergan Grimes, spent for the entire election — and that's after already running more than $8 million in TV ads.

She's not just using that spending advantage to pummel voters with advertising. She's also touting her campaign’s high wages, generous health care and efforts to inform people about changes to voting amid the pandemic — contrasting herself with Booker and underdog Mike Broihier.

“It’s really disappointing that I’m the only candidate in the Democratic primary that has the integrity to lead on these issues within their own campaigns," she said.

But beneath her powerhouse fundraising, there are signs of struggles. McGrath had a bumpy rollout last year, saying in one of her first interviews that she would have supported Brett Kavanaugh’s Supreme Court nomination, only to reverse herself later that day. More recently, Republican governors and Cindy McCain, the late Sen. John McCain’s widow, condemned ads of hers using their images to attack McConnell.

And McGrath has few substantial in-state endorsements, while Booker has been endorsed by prominent Kentucky media and close to two-dozen elected officials.

“There's not a lot of enthusiasm for Amy among Democrats. Charles’ supporters are very enthusiastic,” said one prominent Kentucky Democrat, who requested anonymity to speak candidly.

Still, this Democrat added that she remains a “substantial favorite” to win the primary. Private polling has shown her with a significant, double-digit lead, according to multiple Democrats familiar with the data.

Booker, a first-term state representative, brushed off McGrath’s advantages, arguing he’s “peaking at the right time.”

“The momentum is very real, and it's all across Kentucky,” he said.

McConnell is reveling in a suddenly competitive primary back home. After all, six years ago it was he who faced a credible intraparty challenge from Matt Bevin, the now-former governor.

“It’s been an interesting primary all of a sudden. And honestly, I don’t know what to make of it,” McConnell said in a brief interview.

Republicans say either candidate will be steamrolled in a state Trump will carry handily despite McConnell's unpopularity in polling, though Booker’s liberal positions could make McConnell’s reelection even easier in deep-red Kentucky. Still, Republicans are prepared for an expensive defense if McGrath is the nominee: A super PAC with extensive ties to McConnell has reserved $10.8 million for TV ads in the fall to back the majority leader.

McGrath is positioning herself somewhere in the realm of Sen. Kyrsten Sinema (D-Ariz.), a moderate Democrat elected in 2018 who works with Republicans more than her own party leaders. McConnell himself declined to pinpoint whom he would rather face.

Sanders' and Ocasio-Cortez’s backing helped boost fundraising for Booker, and he raised nearly $1 million in nine days, three times his entire first-quarter haul. Newspaper endorsements and backing from sports radio host Matt Jones gives Booker legitimate in-state boosters outside his base in Louisville.

After coronavirus stalled any effort at toppling McGrath, the protests against police brutality are sparking newfound momentum for Booker.

“How do you run your campaign when you can't go anywhere? And then these protests come around, and I think it helped Charles find his footing and find his voice,” said Jones, who considered running for the seat and criticizes the DSCC. He acknowledged that McGrath remains the favorite but predicted a close finish.

“I don't know that I’ve ever seen a race where somebody has this much money and seems to be struggling,” he added.

Most Democrats declined to criticize McGrath on the record. Even Sanders gave a guarded response when asked why he felt the need to weigh in.

“We’re going to support progressive candidates who are fighting for the issues that we believe in,” Sanders said this week.

Democratic leaders were perplexed by Sanders’ intervention. As Senate Minority Whip Dick Durbin (D-Ill.) put it: “Bernie may have made some promise to someone along the way.”

“She is in the mainstream of Democratic thinking, and I think is very electable in the commonwealth of Kentucky,” said Durbin, who is from neighboring Illinois.

Despite the intrigue in the primary, Kentucky is not central to Democrats’ campaign for the majority. Party officials say that it’s one of the longest shots to flip this election, and the money soaked up by McGrath would arguably go much further in North Carolina, Montana and Iowa.

“Those polls that show it tied are real. But the composition of the undecideds should give us great pause. I am more bullish on South Carolina, Texas — I mean, almost every other race,” said one Democratic senator familiar with party strategy.

McGrath has been squeezed on both sides down the stretch: Booker is running an ad claiming she’s not a “real Democrat” and suggesting she’s too pro-Trump, while McConnell’s campaign released a new ad attacking her support for Trump’s impeachment and calling her “extreme.”

“You can’t run against McConnell from a defensive crouch with a playbook that was obviously cooked up by consultants. You have to perform every day, drive a message and keep him on his back foot,” said Adam Jentleson, who was a top aide to former Senate Majority Leader Harry Reid (D-Nev.). “Only Charles will be able to do that. “

Broihier, a Marine veteran and farmer, is also aiming for voters not sold on McGrath, focusing on rural counties where Booker is less present while also running to McGrath's left, which could complicate projections.

“Kentucky was essentially given a candidate, from the outside,” said Liam deClive-Lowe, Broihier’s campaign manager. “People didn't like that.”

Turnout is uncertain. The May election was delayed due to Covid-19, and all voters are eligible to request mail-in ballots. But only one in-person voting location is open in each county — including Jefferson, home to Booker's base in populous Louisville — and some Democrats fear chaos similar to Georgia.

McGrath’s campaign has joined a lawsuit for more in-person voting options. The extensive mail-in voting could also mean Booker’s momentum is too little, too late.

One former elected Democrat in the state praised Booker's campaign and said his recent endorsements "have taken him from having no shot to having a real shot." But this former official already voted absentee for McGrath and questioned Booker's ability to get his message in front of enough voters in time.

McGrath has had no trouble getting her message out since her grassroots fundraising prowess has let her blanket the commonwealth’s airwaves for months.

“We've been able to build a team to match Mitch McConnell in fundraising, and that’s one of the reasons we’re neck-and-neck with him,” McGrath said. “We’re going to give him a challenge like he’s never seen.”