In addition to all his other mistakes or careless lies, Biden misrepresented facts about the constitution, which he seems not to know much about despite his decades in the Senate. 

This from Power Liine:

This isn’t what’s conventionally described as a gaffe, and it won’t swing any votes, but last night Joe Biden garbled the Constitutional role of the Vice President. I wanted to read the transcript before commenting; here was Gwen Ifill’s question:

Governor, you mentioned a moment ago the constitution might give the vice president more power than it has in the past. Do you believe as Vice President Cheney does, that the Executive Branch does not hold complete sway over the office of the vice presidency, that it it is also a member of the Legislative Branch?

Here is Biden’s answer, in full:

Vice President Cheney has been the most dangerous vice president we’ve had probably in American history. The idea he doesn’t realize that Article I of the Constitution defines the role of the vice president of the United States, that’s the Executive Branch. He works in the Executive Branch. He should understand that. Everyone should understand that.

And the primary role of the vice president of the United States of America is to support the president of the United States of America, give that president his or her best judgment when sought, and as vice president, to preside over the Senate, only in a time when in fact there’s a tie vote. The Constitution is explicit.

The only authority the vice president has from the legislative standpoint is the vote, only when there is a tie vote. He has no authority relative to the Congress. The idea he’s part of the Legislative Branch is a bizarre notion invented by Cheney to aggrandize the power of a unitary executive and look where it has gotten us. It has been very dangerous.

 For a man of Biden’s experience, this is a surprising series of misstatements. First of all, he gets wrong one of the most basic facts about the Constitution: Article 1 establishes the legislative branch, not, as Biden said, the executive branch. This is not exactly an obscure fact… 

Second, it simply isn’t true that the Constitution treats the Vice President only as a member of the executive branch. The Vice President is mentioned in Article II as part of the executive branch, but he is also given legislative powers by Section 3 of Article 1, which establishes the Senate:

The Vice President of the United States shall be President of the Senate, but shall have no Vote, unless they be equally divided.

Vice President Cheney’s "bizarre notion" is in keeping with the plain text of the Constitution.

Finally, Biden misstated the Vice President’s role in the Senate. It isn’t true that he "preside[s] over the Senate, only in a time when in fact there’s a tie vote." The Constitution contemplates that the Vice President will be the full-time President of the Senate, replaced by a President pro tempore "in the absence of the Vice President." It’s true that the Vice President only gets to vote in case of a tie; but, of course, that’s the only time it matters.

If Joe Biden were a high school student taking a test on the Constitution in a government course, he would get a C or a D. Some would say his mistakes were minor, and, as I said, they certainly won’t swing any votes. But it is distinctly odd that a man who has been in the Senate for more than three decades doesn’t understand the Constitutional role of the Vice President with respect to that body.