Environmentalists, labor and women's groups that spent more than $29 million to help House Democrats in 2012 have put up barely a quarter of that amount this year, sparking grumbling among party strategists that is likely to grow louder after Election Day. Democrats, already in the minority, are in jeopardy of losing at least a dozen seats on Tuesday as an onslaught of outside Republican spending has overwhelmed incumbents once considered on track to re-election.