WASHINGTON — Congressional Republicans on Tuesday grilled a health adviser who has demeaned the president's health law, but Democrats highlighted his extensive apologizes and retractions as they tried to limit the political damage. The adviser, MIT economist Jonathan Gruber, told groups in 2012 and 2013 that the "stupidity of the American voter" and a "lack of transparency" were important to passing the legislation without any GOP support. Appearing before the House Oversight committee, Gruber expanded on earlier apologies, repeatedly saying he spoke on topics where he's not an expert.