Perhaps unaware he hasn’t quite won Downing Street yet, Sir Keir then ordered his shadow cabinet not to attend the strikes.
Now the party whose history is interwoven with unions whose support they actively rely on and cause is to fight for the worker have decided to sit this one out, and it is hurting them.
That’s not to say there’s not logic behind it, especially when the Tory party have so desperately tried to label this as “Labour’s strikes”.
By not supporting them, Sir Keir avoids being accused of bringing the country to a halt, and dodges an obvious trap his enemies are so desperate to hit him with.
This response, neutrality in the face of a cause is the theme of his leadership, not saying anything too strong so the focus remains on the Tory party.
But not every fight is worth avoiding, not least when the public seem fairly split on the strikes, as most people agree with better hours, pay and working conditions.
In ordering his shadow cabinet not to attend the strikes, Sir Keir put himself not just against the unions, but against many in his own party.
Now it’s threatening to blow up, with the Labour leader sacking Sam Tarry for turning up on the picket line and doing interviews.
The official line is that is because he did media interviews without sign-off and made up policy on the spot, which is sure to raise eyebrows.
Labour are leading in the polls and all the polling shows Sir Keir beats the favourite Liz Truss in any election.
But at some point, the party will have to decide what they want to do with winning, and offer a vision of why that’s good for the country.
Failing to do so will just cause more infighting, and perhaps lead to a historic fifth term for the Conservatives.