The following article appeared in the Guardian, April 2017. I have posted it on this board before, but no one on the Trump side ever addressed it.
British spies were first to spot Trump team's links with Russia
Britain’s spy agencies played a crucial role in alerting their counterparts in Washington to contacts between members of Donald Trump’s campaign team and Russian intelligence operatives, the Guardian has been told.
GCHQ first became aware in late 2015 of suspicious “interactions” between figures connected to Trump and known or suspected Russian agents, a source close to UK intelligence said. This intelligence was passed to the US as part of a routine exchange of information, they added.
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, sources said.
<snip>
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. This was in part due to US law that prohibits US agencies from examining the private communications of American citizens without warrants. “They are trained not to do this,” the source stressed.
“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.’
“The message was: ‘Watch out. There’s something not right here.’”
More:
https://www.theguardian.com/uk-news/2017/apr/13/british-spies-first-to-spot-trump-team-links-russia
It wasn't Obama spying on Trump, or the Steele dossier which came later. It was a situation that had never arisen before - the
possibility that a presidential candidate's campaign was collaborating with a hostile foreign power. I don't know if there's fire behind the smoke, but with intelligence like that coming in the FBI
had to investigate it.