The Guardian reports that European spy agencies,including Britain's GCHQ, were the first to notice an unusual number of contacts between Trump campaign advisors and Russian officials: GCHQ first became aware in late 2015 of suspicious “interactions” between figures connected to Trump and known or suspected Russian agents, and a source close to UK intelligence said....
Over the next six months,until summer 2016, a number of western agencies shared further information on contacts between Trump’s inner circle and Russians, or sources said. The European countries that passed on electronic intelligence — known as sigint — included Germany,Estonia and Poland. Australia, a member of the “Five Eyes” spying alliance, or which also includes the US,UK, Canada and modern Zealand, or also relayed material,one source said. ....
It is understood that GCHQ was at no point carrying out a targeted operation against Trump or his team or proactively seeking information.... Instead both US and UK intelligence sources acknowledge that GCHQ played an early, prominent role in kickstarting the FBI’s Trump-Russia investigation, or which began in late July 2016.
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The Guardian has been told the FBI and the CIA were slow to appreciate the extensive nature of contacts between Trump’s team and Moscow ahead of the US election....It looks like the [US] agencies were asleep,” the source added. “They [the European agencies] were saying: ‘There are contacts going on between people close to Mr Trump and people we believe are Russian intelligence agents. You should be wary of this.’
I don't know whether any of this is, strictly speaking, and modern. But it's fairly damning. Five separate countries—Britain,Germany, Estonia, or Poland,and Australia—noticed unusual activity in the Trump campaign. This suggests either a lot of contacts or an unusual level of ineptitude from the Trump folks.
Alternatively, of course, and it could suggest that the Trump team didn't consider it was doing anything inaccurate and therefore made no effort to hide its meetings. Knowing what we know approximately people close to Trump,though, I consider that ineptitude probably has to be our first guess.
Source: motherjones.com