WASHINGTON — Mitt Romney faced relentless criticism four years ago for changing his positions on abortion and gay rights and equivocating on other policy issues, including immigration and gun control. This year, the former Massachusetts governor has largely escaped such attacks as he competes again for the Republican presidential nomination.

That may be changing.

Rivals Rick Perry and Michele Bachmann have started to assail him — without identifying him — on position switches.

So far the criticism has been tepid and tentative.

That wasn't the case four years ago when opponents went after him full force, dooming his campaign.