It has been an eventful day in the investigation of Donald Trump's presidential campaign.

Two senior members of Mr Trump's campaign staff handed themselves into the FBI today and have been charged with serious money laundering and tax offences. Separately, another of his advisers has pleaded guilty to making false statements to the FBI.

These are obviously dramatic developments. But what do they mean? Is there actually new evidence to suggest the Trump campaign colluded with Russia? And should Mr Trump himself be worried?

There is a mountain of information floating around and plenty of political spin to go with it, so we've cut through the crap. These are the key points you need to know.

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1. This involves some big fish
Two of Mr Trump's campaign staffers surrendered to the FBI today.

The most senior of them, Paul Manafort, served as campaign chairman from March to August of 2016, and was also campaign manager between June and August. He was the guy in charge of everything.

Mr Manafort resigned amid allegations he received millions of dollars off-the-books while working for the pro-Russian Ukrainian president Viktor Yanukovych.

Richard Gates was the campaign's deputy chairman. He has been Mr Manafort's business partner and right-hand man for years, and shared his Ukrainian connections. Mr Gates retained a role in the Trump campaign after Mr Manafort left, liaising with the Republican National Committee.

A third man, George Papadopoulos, was one of Mr Trump's foreign policy advisers - not such a big deal. He was actually arrested in July, but we only learned of his case today. That fact is crucial, as we'll discuss in a few moments.

2. Most of the charges have nothing to do with collusion
The indictment against Mr Manafort and Mr Gates contains these charges:

• Conspiracy against the United States;
• Conspiracy to launder money;
• Unregistered agent of a foreign principal;
• False and misleading FARA statements;
• False statements;
• Failure to file reports of foreign bank and financial accounts.

"Conspiracy against the United States" sounds rather treasonous, but it is not about collusion. It refers to Manafort and Gates allegedly conspiring to defraud the US. Most of the charges here are essentially about money.

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In a nutshell, Mr Manafort and Mr Gates allegedly worked for a pro-Russian Ukrainian political party, failed to register as foreign agents, were paid tens of millions of dollars under the table, then hid the money and lied to authorities about it.

Both men have pleaded not guilty to the charges, most of which relate to things they allegedly did before joining Mr Trump's campaign.

3. The guy nobody's ever heard of? He's the most important one
Mr Manafort and Mr Gates are the big names here, but the third man, Mr Papadopoulos, is the more interesting story today.

He has already pleaded guilty to making false statements to the FBI, and as part of that plea, has admitted to some incriminating facts.

The short version is that he lied about his interactions with Russians. Here are the important details:

• After joining the Trump campaign, he was approached by people connected to the Russian government, including a professor, a contact from the Russian Ministry of Foreign Affairs, and a woman he believed was related to Vladimir Putin;
• Mr Papadopoulos aided these Russians' efforts to set up a secret meeting between Mr Trump and Vladimir Putin;
• He was told the Russians had "dirt" on Hillary Clinton, supposedly "thousands of emails", long before the public knew;
• Mr Papadopoulos informed at least two senior people in the campaign about his connections, including a "campaign supervisor", who encouraged him to travel to Russia in pursuit of an "off-the-record" meeting. The document does not identify these campaign officials by name, and the trip never happened;
• When he was interviewed by the FBI, Mr Papadopoulos lied about the extent of his relationship with the Russian contacts and the timing of his conversations with them.

To summarise, Mr Papadopoulos actively sought a relationship between the campaign and people he knew to be representatives of the Russian government, with the aim of obtaining incriminating information about Ms Clinton. And other (unidentified) campaign officials knew about it.

4. Papadopoulos is now a co-operating witness
Mr Papadopoulos was arrested on July 27 and signed his plea deal on October 5. It has been sealed from the public for nearly a month. Why?

USA Today's Brad Heath highlighted the critical passage in a court filing from special counsel Robert Mueller's office. Here's the whole thing:

"Defendant has indicated that he is willing to co-operate with the government in its ongoing investigation into Russian efforts to interfere in the 2016 presidential election. Public disclosure of the defendant's initial appearance, however, would significantly undermine his ability to serve as a proactive cooperator. In addition, public disclosure of the defendant's arrest and the accompanying criminal charges may alert other subjects to the direction and status of the investigation."

Let's translate that from legalese to English. After his arrest in July, Mr Papadopoulos appears to have been co-operating with the Mueller investigation. He is referred to as a "proactive cooperator", a term which generally means someone who is doing undercover work - such as wearing a wire. And the Mueller team was worried that revealing his guilty plea would tip off other "subjects" in the investigation.

The fact that his plea has now been unsealed suggests that is no longer a concern. Either Mr Mueller got what he wanted, or there was nothing to get.

If you were a member of the Trump campaign, and Mr Papadopoulos spoke to you about his Russia contacts at any point, you should be worried.

But if you've spoken to him since October 5, you should probably be soiling your pants.

5. No, Trump himself is not directly implicated

There continues to be a disturbing amount of smoke surrounding Trump campaign staffers, but no fire, and certainly nothing that has implicated Mr Trump directly.

Today's events do, however, prove the need for further investigation.

Mr Papadopoulos represents the second clear attempt within the Trump campaign - that we know of - to forge a dodgy relationship with Russia. The other was Donald Trump Jr's meeting at Trump Tower, which he (and Paul Manafort, among others) attended believing he would be offered dirt on Mrs Clinton.

The indictment makes it clear at least three other campaign officials knew what Papadoulos was doing, including the unnamed "campaign supervisor". We don't know who the officials in question are, but special counsel Robert Mueller undoubtedly does.

Mr Trump has repeatedly claimed his campaign had "nothing to do" with Russia. That is clearly false. The question is, to what extent is it false? Only a full investigation will be able to provide the answer.

6. But yes, Trump himself should be worried
There are two important things to note here.

First, we are still at the beginning of Mr Mueller's investigation. We have no idea how much information Mr Mueller is still holding close to his chest, and these indictments are extremely unlikely to be the last.

Second, the charges against Mr Manafort and Mr Gates - and their apparent irrelevance to the question of collusion - should worry the president, not comfort him. They mean the special counsel has adopted a broad interpretation of his mandate.

If Mr Mueller believes the alleged financial crimes of Mr Manafort and Mr Gates are fair game, the same logic will apply to any allegations against Mr Trump.

So if Mr Trump has any dodgy dealings in Russia, even if they are unrelated to the election, he will be in serious trouble. If Mr Trump has illegally avoided paying taxes in the United States - and remember, he still refuses to release his tax returns - he will be in serious trouble. Pretty much everything is on the table.

When he was asked about the scope of the investigation a few months ago, Mr Trump warned Mr Mueller would cross a "red line" if he pried into the Trump family's finances.

If the special counsel does cross that line, don't discount the possibility of Mr Trump firing him, causing a political crisis that would dwarf anything we've seen so far.

This article was first published on news.com.au.