Signing the letter was Boehner, House Majority Leader Eric Cantor, Majority Whip Kevin McCarthy and Rep. Paul Ryan, the chairman of the House Budget Committee and the unsuccessful GOP vice presidential candidate. Rep. Dave Camp, chairman of the Ways and Means Committee, Fred Upton, chairman of the Energy and Commerce Committee, and Cathy McMorris Rodgers, the Republican Conference chair, also signed the letter.Earlier Monday, Obama answered questions on Twitter for an hour as the White House sought to keep up the pressure on the issue. In response to a question about his insistence on higher tax rates for the wealthiest earners, Obama said that "high end tax cuts do (the) least for economic growth & cost almost $1T." By contrast, he said, "extending middle class cuts boosts consumer demand & growth." Obama said he was open to "smart cuts" in spending, "but not in areas like R&D" and education, which "help growth & jobs." He also said he opposes spending cuts that would hurt the disabled or other vulnerable groups. ___ Associated Press writers Matthew Daly and Julie Pace contributed to this report.