The position of Margaret Ferrier really is as untenable as it is possible to be.
The admissions from the Rutherglen and Hamilton West MP are as clear cut a case for resigning as I have seen in a long time.
She is a lawmaker who has become a lawbreaker. She called for the resignation of Dominic Cummings earlier in this pandemic for his interesting interpretation of the Covid rules.
For the sake of consistency she should fall on her sword, lest she want to make a virtue of hypocrisy.
Given the seriousness of the public health messages that her government is promoting, her transgressions hit the top of a one-to-ten scale. That explains the barely concealed fury of the First Minister, who must have thought, not again.
Nicola Sturgeon, despite an initial reluctance, saw the inevitability in the resignation of the chief medical officer Dr Catherine Calderwood some months back for her flouting of the rules. The breaches by one of her MPs are worse, much worse.
Ferrier, who has always struck me as a decent person, should do the decent thing. If she was not thinking straight when she went train hopping, she will be finding that task a tad more difficult now. She will be angry at herself and will know that she has let herself and her party down.
Her party, though, should be the last of her concerns. SNP members are normally well organised in rallying to a colleague in trouble, but even they see the impossibility of her position.
Her judgements have been spectacularly bad. The world is an unforgiving place for a politician who makes a really bad call, as she will be finding out.
The fallout will be hurtful for her and her family and perhaps we should not lose sight of that fact. An error of judgement, no matter how egregious, does not equate to a bad person. She is not, she is flawed, but then again let him who is without sin, etc.
Her prime concern should be the only people who matter: her constituents. Voters absolutely detest the idea that their elected representatives urge a course of action on them, only to choose not to follow it themselves. The reek of hypocrisy can drive the most mild mannered of elector to volcanic fury.
She has let her constituents down. Voters who do not support a sitting MP can nevertheless respect the job that they do and trust them to do it to the best of their ability.
The problem for Ferrier is that respect and trust will be in somewhat short supply. Above all, for the sake of the people of Rutherglen and Hamilton West, Margaret Ferrier should resign now.