Republicans launched TV ads last week aiming to press the advantage, attacking Hickenlooper and hoping to either drag him down before next week's primary or weaken him as he emerges as the nominee.

Hickenlooper — who was recruited and immediately endorsed by national Democrats after dropping his presidential bid — remains the favorite in the tighter-than-expected June 30 primary against Andrew Romanoff, the former state House speaker, according to interviews with a dozen Democrats in Colorado and Washington last week, many of whom requested anonymity to speak candidly. Additionally, they say he maintains an advantage in the general election against GOP Sen. Cory Gardner, especially with President Donald Trump's falling poll numbers over the past few months, and in a state where the electorate tilts increasingly blue.

But Democrats' nominating contest has become much more competitive and fraught in the final stretch. Romanoff launched the first attack ad of the primary Friday, and a new super PAC created only last week immediately released a negative counterattack battering the lesser-known challenger. After his slip-ups, Hickenlooper has rolled out new local and national endorsements aiming to re-establish his pole position.

“Every mistake you make, every stumble, however magnified it is and however many [advertising] points get put behind it, always potentially makes things closer,” said Alan Salazar, who was a strategist in Hickenlooper's gubernatorial office and is now chief of staff to Denver Mayor Michael Hancock. “I can't imagine any of John's mistakes — however magnified they might be — being of such magnitude that they erase the dead weight that Donald Trump is around Cory Gardner.”

Colorado is a must-win state for Democrats as they attempt to seize control of the chamber in this fall’s elections. Democrats hope the race alters course after the primary to focus on Trump and Gardner, who are both underwater in polls. But the recent string of bad news has kept the focus squarely on Hickenlooper and given Romanoff — and Republicans — ammunition to strike.

One Democratic consultant in the state, who requested anonymity to share a candid assessment, described the errors as a “s---show.” The consultant predicted Hickenlooper would prevail and be favored against Gardner, but said “it’s just going to be a lot harder than it should have been.”

Hickenlooper apologized after comments recently resurfaced where he compared political schedulers to slave masters with whips. And he also said he tripped over his words after saying that Black Lives Matter meant “every life matters” during an online forum in late May.

In particular, some Democrats questioned the handling of the Independent Ethics Commission case against him. The hearing was delayed in March because of the Covid-19 outbreak. Hickenlooper offered to testify in person later this year, but the commission went forward with a virtual format over his objection.

The commission issued a subpoena for him to appear and held him in contempt when he did not. Hickenlooper testified the next day, and the commission found that he had violated the state’s ethics laws in two of six charges brought against him.

Democrats have called it a partisan smear because a former Republican lawmaker runs the nonprofit organization that made the allegations, which have been featured in dark-money attack ads. But some Democrats say his campaign should have fought more aggressively.

“This whole thing was a setup from the beginning, and they should have gone after it sooner,” said Laura Chapin, a veteran strategist in the state. She said the ethics ruling was “in the grand scheme of things not that big a deal,” compared to the Trump administration.

“By dragging it out, Hickenlooper people made it last longer,” she said.

One Democrat close to Hickenlooper, who requested anonymity to speak frankly, said he had a “rough couple of weeks” but predicted the ethics headlines would be a “bump in the road.”

“The general election should tighten, and Hickenlooper needs to do more than just successfully raise money," this Democrat said. "He needs to improve his messaging and debate skills, which could become a significant liability for him."

Hickenlooper has focused his bid on his success as governor, pointing to Colorado’s booming economy under his leadership and other successes, including the state’s implementation of all-mail elections, which have become a national flashpoint. His latest TV ad calls the race “a moment for big change,” citing a bevy of success during his tenure.

The former governor has made a discernible effort to demonstrate his fervor for the election, a pushback against his own previous comments about not wanting to serve in the Senate. His campaign declined an interview request for this story.

“There’s no question that I have badmouthed the U.S. Senate as a place that’s broken and, for people that want to get things done, a difficult challenge,” Hickenlooper said in the most recent debate. “But at a certain point you have to decide whether you’re going to be content to sit on the sidelines, or you want to get in the ring with the mud and the sweat, as Teddy Roosevelt said, and be part of the change.”

But Romanoff appeals to primary voters eager for his message of more radical change, including the Green New Deal and Medicare for All. He argues a middle of the road approach doesn’t meet the moment and has said Hickenlooper’s ethics issue is a problem.

"If you break the law, defy a subpoena and get held in contempt, you jeopardize our chances to hold the seat," Romanoff said in a interview.

His campaign released an internal poll from mid-June showing him down 12 percentage points. That is a tighter race than many expected but a challenging margin to overcome in a short period of time — particularly given the poll came after Hickenlooper's struggles and the negative ads against him, and after ballots had already been mailed. Romanoff launched a TV ad attacking Hickenlooper on Friday, which drew condemnation from numerous Democrats including Gov. Jared Polis and Sen. Michael Bennet, who argued it played into Republicans' hands.

Within hours of Romanoff's spot going on the air, a super PAC formed earlier in the week launched its first ad, slamming Romanoff for working with then-GOP Gov. Bill Owens on a restrictive state immigration law. Because the group formed so close to the primary, it won't have to disclose its donors until after the votes are tallied.

Additionally, Senate Majority PAC, which is aligned with Minority Leader Chuck Schumer, is spending $1 million running an ad pushing back against Republican attacks.

And Hickenlooper rolled out endorsements on Saturday from Sens. Cory Booker (D-N.J.) and Elizabeth Warren (D-Mass.). Warren's backing is especially notable: She's trusted by many progressive voters, and she just bucked the DSCC's preferred candidate in Kentucky, endorsing a liberal opponent instead — in a race far less important to Democrats' efforts to reclaim the Senate.

Republicans would clearly prefer to run against Romanoff given his fundraising disadvantage and more liberal positions. As of June 10, Hickenlooper had $5.9 million in cash on hand, more than seven times Romanoff's $792,000; Gardner had $9.3 million.

"We're running a retail campaign because we don't have the resources the other team has got," Romanoff said. "But I'm sure if and when we win the primary we'll find ourselves with a lot more friends and a lot more cash on our hands."

Republicans remain focused on hitting Hickenlooper. Gardner’s campaign is running an ad highlighting the number of times he said he wasn’t “cut out” for the Senate or didn't want the job. The National Republican Senatorial Committee is running ads highlighting the ethics scandal.

“The Democrats are in disarray,” said Rep. Ken Buck, the state GOP chairman, who called Hickenlooper’s ethics issues a “pattern of violations.”

“This is the first time that John Hickenlooper has been tested in politics,” Buck added. “This is really the first time where he will face an opponent who has the wherewithal to do research on the governor and bring out the governor’s record, and there are a number of things that will be revealed in the future that will be very interesting to voters.”

His allies expressed confidence Hickenlooper can right the ship and still has enduring favorability from voters who elected him twice.

“People understand who John is and mistakes that he makes, fumbles here and there,” said Salazar, the former aide. “John is many things. Corrupt is not one of them, and I don't think people are going to believe that about him.”