<p>It's been a cruel summer for Scott Walker and Martin O'Malley.</p><p>That's the assessment of this week's POLITICO Caucus, our weekly bipartisan survey of the top activists, operatives and strategists in Iowa and New Hampshire. Ahead of Labor Day weekend, insiders weighed in on who won -- and who lost -- the summer in their own parties and the results couldn't have been clearer.</p><p>On the Republican side, nearly half of GOP insiders said Walker, the Wisconsin governor, had the worst summer on their side of the aisle.