BE CAREFUL what you wish for. Traders were bored last week and now they have got some excitement. The US equity market suffered its worst trading day in eight months, falling 1.8%, with banks dropping 4%. The Volatility index, or Vix, which recently dipped below 10, jumped above 15. The dollar has lost most of its gains since Donald Trump was elected in November (see chart).

The catalyst for the sell-off seems to be the latest set of political problems for Mr Trump, associated with his relations to Russia. The firing of Jim Comey, the FBI director, was followed in short order by reports that the President has revealed classified intelligence to the Russian foreign secretary, that he had spoken to Mr Comey about dropping the investigation into Mike Flynn, the former national security adviser, the appointment of a special counsel to investigate these matters, and today, a Reuters story that the Trump campaign had 18 undisclosed contacts with the Russians. All this matters, not because Mr Trump is about to be impeached; that is highly unlikely while the Republicans control Congress. It matters because it reduces, or at least delays, the implementation of the programme that caused the "Trump bump" in the first place; tax cuts for the corporate sector and the wealthy, and reduced regulation for the finance sector. Markets are often indifferent to political risk in democracies, feeling that the economic fundamentals are more important. But Simon Derrick at BNY Mellon says the dollar fell during the Watergate affair, the Iran contra scandal of 1986-87 and the impeachment of Bill Clinton over his affair with Monica Lewinsky. And if you want a dramatic illustration of political risk, look at Brazil today, where the stockmarket fell 10% (triggering a halt to trading) and the real fell 6% on allegations about the President Michel Temer; if he loses office, economic reform might stall. The surprise, really, is that hard-bitten traders were naive enough to believe that Mr Trump, a man whom Martin Wolf of the FT memorably described as "a promoter of paranoid fantasies, a xenophobe and an ignoramus" and "grossly unqualified for the world's most important political office" would easily construct, and enact, a coherent economic plan. His campaign was chaotic and so is his governing style. The Republicans in Congress still have an interest in pushing through tax cuts, however (indeed that is why they are still backing Trump) so this dash of pessimism might still be brief.

The interesting thing about the economy is that the Trump election saw a sudden leap in business and consumer confidence but a very lacklustre performance in the first quarter; annualised GDP growth of 0.7% (or as other countries would report it, less than 0.2%). Now sentiment has faded a bit—Bloomberg's consumer confidence index is at its lowest since November—but the second quarter looks set for annualised growth of 4% (1% in quarter-on-quarter terms). That suggests there is something wrong with the seasonal adjustment; put the two together and the economy will have grown 1.2% in the first half (2.4% annualised). Not bad, but not the 3-4% the Trump campaign was talking about. And if the US doesn't grow as fast as hoped, there is less reason for the Fed to raise rates, and thus less yield support for the dollar.

The stockmarket is more optimistic. In part, that is because first quarter earnings have been very strong—they are on track for 14% annual growth, according to SocGen—with the help of a rebound in the energy sector. What will be needed to turn this mini-selloff into a rout would be evidence that earnings growth is set to fade again, either because of problems in the US economy or in China. That will need more evidence than just another hot-tempered tweet from the President.