A letter, from 2011, that then-Vice President Joe Biden sent to Devon Archer - the business associate of Hunter Biden - is being described as a bombshell. 

The letter has been published by the New York Post. 

Dated January 20, 2011, the two-paragraph letter reads, "Dear Devin: I apologize for not getting a chance to talk to you at the luncheon yesterday. I was having trouble getting away from hosting [then-Chinese] President Hu [Jintao]."

Biden continues, "I hope I get a chance to see you again soon with Hunter. I hope you enjoyed the lunch. Thanks for coming. Sincerely, Joseph R. Biden, Jr."

The letter contains the vice presidential seal at the top. And, it also contains a handwritten message from Biden. The rest of the letter is typed.

The handwritten message reads, "Happy you guys are together." Clearly, Biden, here, is referring to Hunter Biden and Devon Archer.

Archer has been making headlines in recent weeks for the testimony that he has provided to the House Oversight Committee. Archer is a former business associate of Hunter Biden, and so he has all kinds of insider information about it.

The big question in all of this is whether Joe Biden had knowledge of or had even participated in Hunter Biden's international business dealings. Joe Biden has maintained that he was not.

But, this narrative is falling apart, thanks, in part, to Archer.

During his House testimony, Archer claimed that Hunter Biden repeatedly - at least 20 times - put Joe Biden on the phone during important business meetings. Many have taken this as proof that Hunter Biden's business consisted of, essentially, selling access to his vice-president father and that Joe Biden was in on it.

Then, last week, Archer told former Fox News host Tucker Carlson that it is "categorically false" that Joe Biden did not know what his son what up to. Archer said, "I think he was aware of Hunter’s business. He met with Hunter’s business partners."

Here, Archer also referred to the letter that Biden wrote to him. Fox News reports that "Archer and Hunter Biden were, at the time, trying to put together a business that dealt with government regulatory measures and were working to create a private equity fund."

Many are now arguing that the letter is further proof - perhaps conclusive proof - that Joe Biden knew about Hunter Biden's business dealings.

The real question is, "How much more proof do we need?" The answer ought to be "none."