The arrest of US President Donald Trump's ex-White House adviser Steve Bannon was a stunning turn of events.

Things had been all quiet until the moment he was arrested on a yacht by US Postal Inspection Service agents on the day former vice president Joe Biden accepted his party's nomination for the presidency.

Bannon pleaded not guilty to a fraud charge during a virtual court appearance.

The case aside, much has since been speculated about the timing of the arrest.

It would be difficult to prove speculation that the decision to arrest the former adviser right at this moment - not earlier, nor later - was deliberately timed by Trump's opponents to give Biden a boost in a final push to oust him.

It would be equally difficult to prove otherwise.

The incident was reminiscent of what occurred in the final weeks of the last election.

Then, just as former secretary of state Hillary Clinton seemed to have recovered from the e-mail scandal that surrounded her, the FBI suddenly announced it was launching a new investigation into the controversy.

That inevitably dealt Clinton's campaign a major blow.

Clinton lost to Trump. So, will Trump lose to Biden?

The New York postal service inspector leading the investigation alleged that Bannon and his associates raised over US$25 million (HK$193 million) to build a section of the US-Mexican border wall.

It is alleged that Bannon skimmed hundreds of thousands of dollars from the donations for personal use despite assurances that the money would all go towards building the wall.

Bannon called the charge a political hit job - and it does appear that, as the US presidential election enters the home straight, incidents of lawful implications have been recurring to take aim at the incumbent.

Though Bannon's guilt or otherwise will have to be decided in court, his arrest could have an immediate effect on voters.

It will remind them of the distasteful fact that Trump's former national security adviser, campaign chairman, lawyer and political confidant was prosecuted for various federal crimes.

It deepens a belief among many that people around Trump were crooks - a point stressed by Biden's deputy campaign manager who responded that "no one needed a federal indictment to know that Steve Bannon was a fraud."

As Americans go to the polling stations on November 3, the case against Bannon will still be ongoing.

Also unfolding in parallel with Bannon's arrest were lawsuits by Chinese-owned apps TikTok and WeChat seeking to overturn Trump's executive orders to ban them from the US market.

By coincidence or not, both argued that the orders violated US laws guaranteeing Americans freedom of speech.

The timing of the incidents was too close a coincidence to take for granted as Trump's opponents may have become restless recently.

First, a poll by CNN - a fierce Trump critic - revealed Biden's lead has substantially narrowed, although the latter still was still ahead in most polls.

Second, Biden's popularity did not bounce as it should have immediately after the Democratic National Convention.

Bannon's arrest was eye-catching - but it is too early to say who will be the winner.

Steve Bannon was Donald Trump's campaign chairman.

Arresting times as poll dramas mount