Boris Johnson suffered the worst rebellion since the election, on what will be the defining issue of his premiership.
The breadth of the Tory revolt over his revised tier system was notable – ideologically from the left to the right of the party, from 1922 grandee to 2019 newbie.
All of this still less than a year after he won an 80-strong majority in the general election.
It ought to be a pivotal moment. Yet it may not prove to be.
Firstly, a win is a win and the government is likely to bank it and change the subject. Secondly Mr Johnson appears, polls suggest, to be more on the side of public opinion.
Voters by and large seem to want tougher measures through the pandemic, and even Labour which abstained on Tuesday is trying to be careful not to look as if it’s on the wrong side of the debate.
The danger for Mr Johnson is that some of the most influential figures voting against the Tory whip cited the manner of his argument as key to their decision to rebel.
They said they were put off supporting the government by Mr Johnson’s over optimistic hints their areas would soon have their restrictions downgraded, a promise they regarded as undeliverable.
They also wish Mr Johnson would be more transparent. There may be no hard evidence on the science behind shutting hospitality. If that is the case, say so, they argue.
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Nevertheless this ought to be a seismic day, but may not necessarily prove to be.
2021 will all be about the vaccine. If the government manages to roll it out to most of the population in an orderly or timely way, that could be transformational.
Labour is acutely conscious that this would mean messy moments like today, for all the Tory infighting, could easily be forgotten be a grateful public.