Whatever culpability you imagine Nancy Pelosi has regarding Jan 6, Mitch McConnell would share the same. Nonetheless, neither of them bears the culpability you imagine, because they don't have the kind of oversight you are implying. The Capitol Police are controlled by a board of the Capitol Architect, and the Sergeants at Arms for the two chambers of the Congress. The Capitol Architect is appointed by the President for a 10 year term and the Sergeants at Arms are appointed by the Speaker of the House and the Senate Majority Leader. But the Speaker of the House and the Senate Majority Leader do not control the Capitol police as you imagine, nor should they if you think about it.

I think there was a failure in security that day, but it's still a big question as to exactly what that was. This is part of the scope of the Jan 6 Committee, and we should get some answers here this year.