Senior ministers are "absolutely furious" about his resignation and departure from government.
Some ministers believe the claims in his letter are "just not true because he is well aware that the welfare changes have always clearly been about saving money as well as improving the systems".
It's suggested that his central motivation is the EU referendum, and, for others who are supporting him, a strategy to kill off George Osborne's hope of taking over from David Cameron.
IDS's team is adamant that his exit is entirely about the handling of PIPs (Personal Independence Payments) and nothing to do with the EU.
Whatever the truth, it is very dangerous for a political party to be so publicly divided, and, on a very simple level, for its members to be so angry with each other.
It's not just Iain Duncan Smith who's angry.