Johnsonism’s political theory is that the Brexit revolt created an opportunity for the right-wing party that led the rebellion to consolidate support among the working-class voters who provided the electoral foot soldiers. That opening is time-limited. Once Mr. Johnson has executed Brexit, he’ll need to give those voters some other reason to support the Tories. His economic theory is that by aping the left-wing policies those voters have always supported but implementing them more competently, his party can bring those voters permanently into the fold.

Similarly, Mr. Rubio, seeing how Mr. Trump has activated new segments of the electorate for Republicans, is trying to devise some policy platform to retain those voters once Mr. Trump is no longer on the ballot. The solution is to copy much of the language and some of the policy views of the left so as to avoid alienating those new voters.

The most telling manifestation of this, from both Mr. Johnson and Mr. Rubio, is their approach to productivity and investment. One of their insights is entirely traditional-conservative: Only by boosting productivity can an economy deliver employment and wage growth. But then they steal the first and worst page from the left’s playbook: the conviction that the interests of capital and labor inevitably conflict in this sphere.