To be fair, Baylor, Blair had an interesting interpretation of the facts (WMD turned out to mean battlefield munitions, for example).
Thatcher will be treated far better by history than Blair. Leaving aside greater competence, she'll always have many rightwingers on-side. Brown will always have at least some leftwingers on-side. Who will Blair have? It's hard to see many, right or left, backing him. Those disinterested in politics generally will remember only Iraq (and that's fair enough, it's the defining feature of his decade long premiership).
As an aside, it's curious that of recent PMs John Major appears to be remembered surprisingly fondly. Perhaps it's because he was a fundamentally decent bloke, whereas those before and after him appear either too harsh, or smarmy chancers.