The row between Jeremy Corbyn and Jo Swinson is one of the most important in modern British political history.
The Labour Party and Liberal Democrat leaders are at odds over who might lead an emergency government of national unity to stop a UK departure from the EU without a deal. If the prime minister loses a vote of no confidence in a fixed term parliament, the opposition has 14 days to form a new government.
It is distinctly possible that Boris Johnson will lose such a vote. His working majority in the House of Commons is in effect one. That is when the DUP is included. It only takes a small number of Tories to side with such a motion. There are at least 20 hardcore Tory opponents of no deal. Several of them face deselection as Conservative candidates in any event, so they might feel that they have nothing to lose.
There are a similarly small number of determined Labour Brexiteers, including Kate Hoey, but it is hard to envisage many of them defending the government in such a motion. Brexit backers hope then the opposition cannot form an alternative (which would be more likely if Sinn Fein MPs sat). In the absence of an alternative, Mr Johnson might be able to push an election past Brexit on October 31.
This will be perilous outcome for everyone. But Dublin demanded the Irish border be tied down in perpetuity before a future UK-EU relationship was agreed, which led to a backstop that made the Withdrawal Agreement toxic.