Steve Kornacki, the latest source of misery for New Jersey Gov. Chris Christie, has been getting worried messages from relatives over the past few days.

“My family has been sending me all sorts of texts about being careful,” the host of MSNBC’s weekend morning program, Up with Steve Kornacki, said on Monday. On Twitter, the National Journal’s Ron Fournier predicted--jokingly--that Kornacki “will be sitting all month in traffic.” And The Daily Kos’s Greg Dworkin, a Connecticut Democrat, tweeted mock-threateningly: “Nice cable show you got there, Steve. Shame if something happened to it.”

“I haven’t really slept,” Kornacki told me. “I was going to sleep during the day, but now I’m not going to be able to. I’m still working the phones, trying to see what else is put out there--if there are any more angles in particular on this Christie story.”

The embattled governor and his administration were already facing multiple investigations over the politically vindictive George Washington Bridge traffic debacle last September as he was breezing to his landslide reelection. But Kornacki, 34, managed to increase Christie’s troubles significantly on Saturday with a blockbuster interview featuring Hoboken Mayor Dawn Zimmer, a Democrat who, until now, anyway, had been a conspicuous cheerleader of the Republican governor.

On Kornacki’s show, Zimmer accused Christie and his minions of refusing to release millions of dollars in Superstorm Sandy recovery aid to her flood-ravaged city on the banks of the Hudson River unless she fast-tracked approval and lucrative tax breaks for the construction project of a supremely well-connected real estate developer. She offered to take a lie detector test and testify under oath.

“I wasn’t sure how much play it would get, but I knew it would cause a stir when I walked in Saturday morning to do the show,” Kornacki said about Zimmer’s allegations, which were supported by emails from lobbyists and New Jersey state officials and other apparently corroborative documents, including the mayor’s messily scribbled private diary. “I wasn’t sure how big it would be. I figured it would have an impact. It was a bigger impact than I expected.”

Kornacki’s scoop--obtained with help of New Jersey sources dating back to his years as a Hoboken resident and reporter for a political web site owned, serendipitously, by future Christie Port Authority appointee and bridge scandal principal David Wildstein--turned out to be explosive. It was front-paged in Monday’s New York Times and the mayor, after repeating her allegations Sunday on CNN, doubled down by telling her story to the U.S. Attorney in Newark.

Along with the bridge incident, it’s another active criminal investigation for federal prosecutors, and could potentially derail not only Christie’s governorship and his chairmanship of the Republican Governors Association, but also his plans to run for president in 2016.

Team Christie has reacted with a ferocity reserved for the deadliest of threats, impugning the “partisan” motives of Mayor Zimmer and MSNBC, denying her allegations about a quid pro quo, and trotting out Lt. Gov. Kim Guadagno--whom Zimmer identified in her diary and television appearances as the official who took her aside and strong-armed her in a Hoboken parking lot last May--to essentially call Zimmer a damned liar. This, in a press conference Monday at which Guadagno looked like she was making a hostage video and declined to take questions.

“From the personal standpoint, the weird thing about all this is that I know so many of the players in this story so personally from my New Jersey days,” said Kornacki, who toiled for Wildstein’s web site, a precursor to PolitickerNJ, in the early 2000s. “This story is national in scope but involves relationships in Jersey that go back ten, twelve years. ‘Weird’ is one word to describe it. Professionally, it’s right-place, right-time.”

Despite his Rolodex of Jersey connections, Kornacki didn’t know Zimmer. “I might have met her covering politics, but if I did I don’t remember,” he said. He first heard about her problems with the Christie administration early last week and made an appointment to see her in Hoboken, where she confirmed what he’d been hearing and offered up her documents.

The mayor dispatched an aide to take Kornacki on a tour of the proposed construction site in a warehouse district in the north part of town, where the Rockefeller Group, the venerable developer that built Manhattan’s Rockefeller Center, had purchased four acres and wanted substantial tax breaks to erect an office tower. The developer is represented by the powerful law firm of Christie ally David Samson, who also figures prominently in the GW Bridge traffic jam scandal as Christie’s hand-picked chairman of the Port Authority of New York and New Jersey.

Despite intense lobbying--including, Zimmer alleged, from Christie’s commissioner of community affairs, Richard Constable--the desired tax breaks for the Rockefeller Group have not been forthcoming.

“I saw the land in question, the development that was supposed to occur, and the mayor was willing to provide documents,” Kornacki told me. “So it was a process of getting those documents, and reviewing them. Also, she wasn’t entirely clear from the beginning that she wanted to come on the air and make the accusations. She wasn’t sure until Friday morning that she wanted to do it. We’d had a different show planned.”

There followed two meetings, totaling three hours, with MSNBC in-house lawyers and standards and practices staff. “I guess it was the longest meeting with lawyers I ever had in my life,” Kornacki said. “We wanted to make sure we were confident in the documents we had. We wanted to subject them to a lot of scrutiny on our end before it was something we aired. We wanted to be able to show the documents and we went through every assertion in her story.” Zimmer’s account, he added, “passes the plausibility test.”

Her private diary was an especially compelling piece of evidence. “I think she was a little embarrassed about her handwriting and having it being seen on national television,” Kornacki said. “Obviously, we can’t do carbon dating on the pages to make sure that this was an authentic contemporaneous account in her diary, and we were trying to look for anything that could tip us off one way or the other on whether this was legitimate or not. The handwriting was one of the things that made it more authentic in our minds.”

After the fateful encounter with Guadagno during a morale-boosting visit to a ShopRite store in Hoboken, Zimmer scrawled in her diary that the lieutenant governor pulled her aside “and says I need to move ahead with the Rockefeller project. It is very important to the governor. The word is you’re against it and you need to move it forward or we’re not going to be able to help you [with Sandy aid]. I know it’s not right. These things should not be connected but they are. If you tell anyone I said that, I will deny it.”

Needless to say, MSNBC has been touting Kornacki’s scoop in wall-to-wall coverage, and he appeared Monday night on All In with Chris Hayes to punctuate his journalistic coup.

“I didn’t do it with the intent of ‘Let’s get Chris Christie. Wouldn’t it be great to see him fall?’ Or anything like that,” Kornacki told me. “We got a serious accusation and we found this story, and we’re not making a judgment that we guarantee that this is what happened.” He added that since the weekend, “I’ve been going back in my mind and a little bit this morning, just to make sure--running back the sequence of events, to make sure I feel good about putting it on the air. And I do.”