The Democratic party has won both chambers of US Congress in the midterm elections, wresting control from the Republicans. With Donald Trump still in the White House until 2028, the result has raised expectations of political gridlock.

Analysts at the US investment bank Stifel, for example, have predicted that gridlock is “the most likely policy outcome”. Ahead of the elections, Trump warned he would block all legislation sent to him by a Democrat Congress, saying he might become “Mr Veto”.

He has since softened his tone. On election night, Trump told journalists he was “absolutely willing” to accept the results, adding: “We’ll work with the Democrats, and we’ll, you know, look forward to working with them.” He has still promised to use his presidential veto for “things that are insane”.

History casts doubt on the gridlock prediction. Our analysis of past US Congresses suggests that, while losing both chambers means more opposition for the president, it could also reduce partisan friction between the House and Senate.

Since 1949, the opposition has controlled only the House in seven Congresses, compared with 15 in which the opposition has controlled both chambers. In another 15, the government was unified, with the president’s party controlling both.

As shown in the figure, opposition control of both chambers need not mean less legislation. Opposition-controlled Congresses have passed roughly as many laws as unified ones, and more “important” laws than those in........

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