Jonathan Chait argues that Romney was doomed to lie:

It’s Romney’s bad luck that fate has dictated his only path to the presidency lies in being a huge liar.

It’s tempting to accept this explanation, but it confuses two very different things. Romney was at odds with movement conservatives on most issues before he started reinventing himself for his first presidential run, so it’s true that he had to abandon most of his previous views in order to become acceptable to most Republican voters. This makes him exceptionally unprincipled, but this didn’t require an unusual degree of dishonesty. Romney could have reinvented himself as he did without insulting everyone’s intelligence with claims that he has been “as consistent as human beings can be.” He could have acknowledged his changed positions instead of providing torturous explanations in which he never admits having been wrong, and he could have run presidential campaigns that didn’t involve him attacking his rivals for their lack of conservative zeal.

It’s possible that being exceptionally unprincipled on policy for the sake of political ambition makes it easier to be dishonest about all sorts of things. Both make Romney untrustworthy in different ways, and they both stem from a desire to overcome inconvenient realities. Maybe his thinking goes something like this: “If it makes sense politically to reinvent myself to get elected, why wouldn’t it make sense to make things up about the rest of the world, too?” There are two kinds of lies that Romney tells most often: far-fetched explanations that try to reconcile his past views with those he currently holds, and demagogic distortions of what the Obama administration has done. The former are obnoxious, but it’s the latter where Romney excels as a politician at war with truth. Romney wasn’t fated to make attacks on Obama’s foreign policy one of the central themes of his campaign, and it was his choice to attack on this subject that led him to make many things up out of thin air to support his criticism.