In the past week, former New York Mayor Rudolph Giuliani, now the chief lawyer and principal spokesman for President Donald Trump's legal team, has offered arguments more harmful to Trump than helpful. In a series of combative, disjointed and logically challenged television rants, Giuliani has essentially argued that Trump did not engage in any conspiracy with the Russians for them to provide help to his campaign and that even if he did, it wasn't criminal.

In making this argument, Giuliani has played a word game in which he has effectively created a straw man and then denied it's real because it's made of straw. He has done this by avoiding the use of the word "conspiracy," substituting the word "collusion" and then arguing that there is no crime of collusion and therefore Trump did not commit a crime. This is an argument based on a false premise.

Here is the back story.

When the FBI received word from a former British intelligence source in June 2016 that Russian intelligence agents might be providing assistance to the Trump campaign, it began an investigation of the campaign. After the British source gave the FBI a dossier that alleged salacious behavior by Trump in Moscow in 2013 -- behavior he has denied -- and purported to corroborate awareness of the behavior by Russian government officials, the FBI used the dossier as part of a presentation to the Foreign Intelligence Surveillance Court, which authorized surveillance of the Trump campaign.

Because one of the Trump campaign officials under surveillance, Jeff Sessions, became the attorney general in January 2017, he recused himself from the investigation, and the Department of Justice appointed former FBI Director Robert Mueller special counsel to head the investigation independent of the attorney general.

Mueller discovered dozens of contacts between the Trump campaign and Russians, many of them Russian intelligence agents. Mueller's grand juries have indicted over two dozen Russians, some Russian intelligence officials, for interfering with the 2016 presidential campaign, and President Trump imposed heavy financial sanctions on many of them.

Mueller also discovered the existence of a June 2016 meeting in Trump Tower in New York between high-ranking campaign officials and Russian agents. When The New York Times revealed the meeting a year after it took place, the Trump folks claimed that the meeting was about the difficulties Americans were having adopting Russian children. Then emails emerged showing an offer to Donald Trump Jr. by a Russian agent to meet and provide help to the campaign in the form of dirt on Hillary Clinton. This was dirt allegedly obtained by hacking into her campaign's computers. This was an offer that Don Jr. accepted.

The president has denied any knowledge of this meeting until it emerged publicly in July 2017, and Don Jr. has testified under oath before Congress that his father did not know of the meeting until the media revealed it. But last week, Michael Cohen, a lawyer who represented Trump for the 10 years preceding his inauguration and whose office was three doors down a hall from Trump's, told Mueller and the media that Trump knew of the meeting beforehand and encouraged his campaign folks, including Don Jr., to make it happen.

Is any of this unlawful? That question brings us back to Giuliani.

In Giuliani's zeal to represent his client, he has unleashed vitriolic verbal attacks on the credibility, morality and ethics of Cohen, using words and innuendo too lurid to recount here. Yet the ferocity of Giuliani's attacks is now a problem for Trump. That's because the rules of legal ethics prohibit lawyers from attacking the credibility of likely witnesses against their clients outside the courtroom. This is especially so for government witnesses.

Government witnesses meet with prosecutors and testify before grand juries in secret. When defense counsel attacks those witnesses in public, the government often views that as witness tampering -- behavior that gives witnesses pause before testifying by freighting or threatening them. When defense counsel did that to government witnesses in cases that a young Rudy Giuliani prosecuted, he persuaded judges to remove those lawyers from the cases. That is the danger that confronts Giuliani and Trump now.

If Mueller has enough ammo (all of it from Giuliani's mouth) to persuade a federal judge to bar Giuliani from continuing to represent Trump -- and it appears he does -- whoever replaces Giuliani will need to review and understand more than 1.4 million documents that the White House and the Trump campaign have surrendered to Mueller. That will be an enormous burden and a major financial, political and legal setback for Trump.

The case Mueller is investigating is not about collusion. Collusion is a Hollywood and a media word. The case is about conspiracy -- and Giuliani knows this. A conspiracy is an agreement to commit a crime as a result of which at least one of those who agreed took at least one material step in furtherance of the agreement. Stated differently, Mueller is investigating an alleged agreement between Russian intelligence agents and Trump campaign officials for the Russians to provide dirt on Clinton to the campaign. The dirt need not have arrived -- and whatever may have arrived need not have been dirt -- for the crime of conspiracy to have taken place, because the essence of conspiracy is an agreement, whether consummated or not.

In one of his more bizarre rants on Fox News Channel early this week, Giuliani said there may have been a meeting at Trump Tower to plan the meeting with the Russians. Why would he reveal this? Because Mueller knows it and will reveal it. And both know that such a meeting would be the beginning of an agreement, as well as a material step in furtherance of it.

Sometimes even famous lawyers do more harm than good to their clients.