Democrats Can't Figure Out Why the Federal Entities Who Infiltrated Groups Involved in Jan 6th Did Not Prevent Jan 6th.

The introduction of this CNN story speaks volumes:

The January 6, 2021, attack on the US Capitol was “essentially planned in plain sight on social media” and yet the FBI and Department of Homeland Security appeared to have “completely dropped the ball,” a Senate committee concluded in the latest highly critical assessment of the security failures.

A new report released by Democrats on the Senate Homeland Security Committee paints a freshly damning portrait of various intelligence failures by the FBI and DHS Office of Intelligence and Analysis, agencies tasked with preventing domestic terrorism.

Internal communications from both agencies, obtained by Democrats on the panel, reveal new details about how top officials either ignored or dismissed clear indicators of potential violence by pro-Trump actors ahead of the US Capitol attack – leaving law enforcement unprepared for what ultimately unfolded that day.

Here's one possible explanation as to why "top officials either ignored or dismissed clear indicators of potential violence":

To summarize: if the FBI and DHS had infiltrators amongst the Jan 6th protestors, egging them on to breach the Capitol, why would departments themselves try to stop it? To do so would run counter to their objective and/or reveal their involvement. 

But it's way easier to label these departments as incompentant than complicit.