On Wednesday, Donald Trump looks set to become the third US president to be impeached. Nancy Pelosi’s Democrats took less than three months from launching the inquiry to its conclusion at which Mr Trump will be indicted on two counts: abuse of office and obstruction of Congress. But for all Ms Pelosi’s clarity, Mr Trump’s impeachment is dangerously one-sided.

In January, the Senate will hold an abbreviated “trial” in which the most senior juror, Mitch McConnell, the Republican leader, has admitted he will co-ordinate every step with Mr Trump. Holding a president to account is the US constitution’s ultimate remedy for a renegade executive. In this case, however, the system will not even make a pretence of weighing the evidence. Mr Trump has all but been acquitted of abuses for which he is self-evidently guilty. The US mechanism of checks and balances will thus be left weaker at the end of the process than at the start.

For the most part, Democrats have handled the process fairly. The main criticisms are that they have drawn up the articles of impeachment too narrowly and been in too much of a hurry. The two are linked. Had Ms Pelosi gone beyond Mr Trump’s Ukraine allegations to include the obstructions of justice listed in Robert Mueller’s Russia report, the process would have lost speed and become more complex.