Since Donald Trump's election a shadow has hung over his administration - a federal investigation into possible collusion between the president's campaign and Russian agents.

Robert Mueller, the stern former FBI director now leading the investigation, has charged dozens of individuals with crimes ranging from election interference to fraud along the way.

Mr Trump has denounced the probe as a "witch hunt" - a view held by a number of leading Republicans.

However the alleged crimes detailed by Mr Mueller's team so far indicate the potential extent of the attempt to interfere in the 2016 presidential election.

With the wide-reaching investigation reportedly aiming to reach its conclusion by September 1, here is a timeline of the key events to date.

May 2016