New York (CNN Business) A version of this article first appeared in the "Reliable Sources" newsletter. You can sign up for free right here.

Something big is happening. Just look at Monday night's home page headlines:

Politico: "Dems moving to formally condemn Trump as impeachment fever grows

And a second headline from WaPo: " Pelosi quietly sounding out House Democrats about whether to impeach Trump, officials say"

Manu Raju's insights

"It's clear the impeachment terrain has shifted," CNN's senior congressional correspondent Manu Raju told me shortly after 10pm ET Monday. "Dems have been looking for a triggering event to get behind impeachment and now have found one — especially if it turns out Trump sought to withhold military aid in exchange for a Ukraine probe into the Bidens. That's easier to message and for the public to see as a clear abuse of power, Dems believe, than the details of the Mueller report that Trump has muddied."

On Monday evening, seven key freshman Dems came out with an op-ed signaling support for impeachment. Raju said this is another sign that Dems are nearing a tipping point: "Pelosi has sought to protect vulnerable freshmen — her first priority — but as more come out for impeachment, many believe she will too. As one Dem put it to me today, Pelosi wants to be the leader of the parade — not the follower of the parade."

"The dam is breaking"

It's been hard to keep up with all of the developments in the past few hours. "The dam is breaking" on impeachment, an unnamed House Dem told the NYT's Jonathan Martin. "I can't overstate what a shift there's been," Politico's Heather Caygle tweeted Monday night. "Some members have been wanting to back impeachment for a while and wanted cover. For others, this really was the last straw. The most important thing is that leadership recognizes this and is shifting strategies as a result."

On MSNBC, Ali Velshi spoke of a "growing tide for impeachment." Even Laura Ingraham, speaking around the same time on Fox, said this scandal is a "shot in the arm to the impeachment movement," even though her guests all defended Trump and tried to spin away damning Ukraine-related details...

The House Dem caucus will meet on Tuesday

"The House Democratic caucus will meet Tuesday afternoon," per Raju's story . A leadership aide told CNN that the topic is likely to be about the next steps on investigations..."

FOR THE RECORD

-- Susan Hennessey's warning: "No one should kid themselves or feel gleeful in this moment. Impeachment always tears at the fabric of a nation. The only thing that is more destructive would be to not impeach when the Constitution demands it." ( Twitter

-- Michael Gerson's rousing message: "Opposing Trump's corrupt abuse of power is today's form of patriotism..." ( WaPo

-- Because I know you're wondering: Sean Spicer survived the first elimination round of the "Dancing With the Stars" season... The Supremes' Mary Wilson is heading home... ( ET

"Biden wages war on Hunter-Ukraine reporting"