I don't by that 'insecurity' story about the reason for the Watergate break-in. I don't know what it could be, but no spooks are stupid enough to mount a black bag op. for 'a political edge'.
I think that the FBI and CIA suspected the DNC of collaborating with Chinese or Russian spies in the call girl business the DNC hosted for visiting Senators, congressmen, dignataries, etc. Once the break-in went tits-up, Nixon would have been bound by national security and law not to reveal it's purpose. Leaving the press free to make up what ever other stories they like.
Dean ordered the break-in, according to Liddy. There is Liddy's summary of his version here.