Analysis by Chris Cillizza, CNN Editor-at-large

(CNN) -- Of late, a particularly misleading canard has emerged among those seeking to discredit the special counsel investigation being led by Robert Mueller: That the former FBI boss has moved well beyond his original mandate to probe Russian interference in the 2016 election and the possibility of collusion between the Trump campaign and the Russians.

Former New York City Mayor Rudy Giuliani tried to make just that argument during a sitdown with CNN's Dana Bash on "State of the Union" Sunday.

Here's one exchange on that point:

GIULIANI: All that it means is an investigation that we thought was rigged was rigged from the very beginning. It never should have -- it never should have started.

BASH: But if you're saying...

GIULIANI: Because there was no evidence of collusion.

And, here's more Giuliani when asked whether he thought the Mueller investigation was legitimate: "I did when I came in. But now I see -- I see 'Spygate.' I see the judge, Judge Ellis, in Manafort saying ..."

Giuliani is referring there to comments made by the judge in the case against one-time Trump campaign chairman Paul Manafort, in which Judge T.S. Ellis accused prosecutors of using the charges of financial impropriety regarding Manafort's dealings in the Ukraine solely as cover for their efforts to turn Manafort against Trump in the broader Mueller probe.

The problem with that argument is that it seemingly ignores the fact that Mueller was given wide latitude by Deputy Attorney General Rod Rosenstein to pursue any crimes or potential crimes he came across.

Lucky for us, the document establishing the special counsel is readily available on the Internet. Here's the relevant passage:

"The Special Counsel is authorized to conduct the investigation confirmed by then-FBI Director James B. Comey in testimony before the House Permanent Select Committee on Intelligence on March 20, 2017, including:

(i) any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump; and

(ii) any matters that arose or may arise directly from the investigation; and

(iii) any other matters within the scope of 28 C.F.R. § 600.4(a).

(c) If the Special Counsel believes it is necessary and appropriate, the Special Counsel is authorized to prosecute federal crimes arising from the investigation of these matters."

Almost everyone focuses on "(i)" of that statement: "Links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump."

But that's only a single part of Mueller's broader mandate, which also includes:

"Any matters that arose or may arise directly from the investigation"

"The authority to investigate and prosecute federal crimes committed in the course of, and with intent to interfere with, the Special Counsel's investigation, such as perjury, obstruction of justice, destruction of evidence, and intimidation of witnesses; and to conduct appeals arising out of the matter being investigated and/or prosecuted." (That's language from the portion of the Code of Federal Regulations referenced in (iii).)

So when people like Giuliani try to make the case that Mueller has exceeded his mandate, they are simply ignoring the text above.

Yes, this investigation was -- no matter what Trump allies say -- begun as a result of concerns about George Papadopoulos' susceptibility to a Russian influence campaign. And its original focus was on Russia's efforts to meddle in the 2016 election and the possibility that members of the Trump team were actively involved in aiding that effort.

But there was never a constraint on Mueller to adhere only to those questions. He has always had the mandate to explore "any matters that arose or may arise directly from the investigation," which means that potential obstruction related to the firing of former FBI Director James Comey, the financial issues found around Manafort and lots and lots of others issues fall under Mueller's umbrella.

Giuliani and others can not like that. But Mueller's mandate comes from Rosenstein. The paper trail tells the tale.