Well, here we are. This week brought the news that CNN had cut ties to Donna Brazile, the interim chairwoman of the Democratic Party and a longtime paid political analyst for the network. They parted ways after leaked emails indicated that she had shared with Hillary Clinton’s campaign some possible questions for CNN-sponsored candidate events during the primaries.

It took 20 years, but the warnings have come true — the contamination has spread and the patient is looking sickly.

The mess with Ms. Brazile draws to a close a campaign season that tore at the foundation of the wall Mr. Frankel wrote about. It started with news that Mr. Stephanopoulos had donated $75,000 to the Clintons’ family foundation; went on to include CNN’s hiring of the former Trump campaign manager Corey Lewandowksi as an analyst, even as he continued to be paid a “severance” from the Trump campaign; and saw Sean Hannity of Fox News (who famously intoned “I’m not a journalist”) emerge as an informal adviser to the Trump campaign.

But Ms. Brazile’s entanglement took it all to a newly scandalous level.

As Jeff Zucker, the CNN president, told his journalists in a conference call on Tuesday morning, the disclosure of Ms. Brazile’s assist to the Clinton campaign threatened to undercut all their hard work this year. Worse, for the industry at large, it played into Donald J. Trump’s accusations that the mainstream media was colluding with Mrs. Clinton to deliver her to the White House.

The whole thing stinks. But the moment will be wasted if it does not prompt the networks to reset the boundaries between their newsrooms and their paid political operatives, if not end these arrangements altogether.