USSC Research Director Jared Mondschein tells ABC's The World that an FBI raid on a former president's property is no small matter - in fact it is unprecedented. "This is likely to be signed off by FBI Director Christopher Wray who is a registered Republican and was appointed by Donald Trump and it was likely to be signed off by Attorney General Merrick Garland who was President Obama's nominee for the Supreme Court," Mr Mondschein said.

"The issue here is that it's not just document retention, it's likely to be something much bigger than that for them to take this unprecedented step because it's not very easy to get a Federal search warrant let alone getting one for a former US president.

"Ultimately we have more questions than answers on this. There has to be a high degree of probable cause to merit this. What kind of evidence does the FBI have? Why are they doing this now? What specifically were they looking for? Did they find it?

"And considering it's extremely unlikely you'd find a jury that would convict President Trump in a criminal trial we probably won't know these answers for a long time."