Donald Trump used the Hillary Clinton email scandal as a major weapon in a bid to help him win the White House and regularly tweeted about it during his presidential campaign.

Now, emails are once again at the centre of a fresh scandal in Washington following the release of Donald Trump Jr's correspondence with a Russian lawyer who claimed to have information damaging to the Clinton campaign.

Coincidentally, on the same day (9 June 2016) that Trump ramped up his assault over the email scandal on Twitter, his eldest son Donald Trump Jr was meeting the Kremlin-linked lawyer in Trump Tower.

Reviewing the history of exchanges, then presidential candidate Donald Trump mentioned Clinton's emails on a handful of occasions in 2015, and in his tweets he criticised Clinton for her mishandling of a private server, often by simply retweeting other commentators who had spoken about it.

In September 2015, he went silent on the matter. It was almost 10 months later when he brought up the subject again during a Twitter exchange with Clinton.

On 9 June 2016, Trump began by criticising Obama and Clinton, saying: "Obama just endorsed Crooked Hillary. He wants four more years of Obama—but nobody else does!"

"Delete your account," was Clinton's terse reply.

Trump shot back with: "How long did it take your staff of 823 people to think that up--and where are your 33,000 emails that you deleted?"

This was the first in dozens of email-related tweets that had a very different tone to the ones issued a year earlier, and foreshadowed a pillar of the Trump campaign's attacks on Clinton.

Now, Trump Jr has offered to testify under oath following his release of email exchanges that confirmed the meeting during the 2016 US election campaign.

One of the central emails in the release was sent on 3 June, which said there was information that "would incriminate Hillary and her dealings with Russia and would be very useful to your father [Donald Trump Sr].

"This is obviously very high level and sensitive information but is part of Russia and its government's support for Mr Trump."

Trump Jr responded saying: "If it's what you say I love it especially later in the summer."

The emails showed that he was ready to accept information from foreign agents to help his father win the White House, which directly undermines the previous statements of the White House, who in recent months have been adamant that no-one inside the Trump campaign had any contact with Russians.

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Donald Trump, Jr. (R) greets his father Republican presidential nominee Donald Trump on October 9, 2016 in St Louis, Missouri. Getty Images