I don't think this is the final nail in the coffin, it's the first nail in the coffin.
Things will only get worse for him from here on out.
Yeah. This is more an "end of the beginning". The pretense that Trump could rise above his history, and be anything but a reality-tv President is done now. It's the final nail in his honeymoon, not his presidency. More and more people, including himself, are giving up on pretending he could do the job.
But it's not the "beginning of the end". That will only happen when his support utterly collapses and whatever process finally forces him out gets rolling. When articles of impeachment go to the floor, when the Cabinet removes him, the generals launch a coup, or he gets defeated for the GOP nomination.
Whatever happens, I don't think he'll go quietly, though. I forsee a police cordon around Mar A Lago or the White House before he gets perp walked.