MANCHESTER, N.H. – Scrambling to salvage his presidential campaign, Joe Biden escalated his criticism of Pete Buttigieg on Saturday, mocking Buttigieg’s experience as a small city mayor and cutting down the comparisons Buttigieg has drawn to the last Democratic president, declaring: “This guy’s not a Barack Obama.” Biden’s biting attacks on Buttigieg’s relatively thin resume mark a new, more aggressive attempt to slow the momentum of the youngest candidate in the Democratic field.