Is America’s election vulnerable to hackers? The Federal Bureau of Investigation, which is examining alleged Russian hacking of Democratic party databases, thinks so. Cyber security analysts have issued stark warnings of the potential for interference.

State-backed Russian hackers are suspected to have downloaded the voter databases of Arizona and Illinois. Many other electoral registers are thought to be badly exposed. The signals are too loud to ignore.

Russia has a record of carrying out black operations in other western democracies. Donald Trump, the Republican nominee, has warned the November election could be rigged. President Vladimir Putin could hardly ask for more. If Russia wished to sow doubt about America’s electoral integrity — and there is little question Moscow does — the opportunity is there.