why is the u.s. presidental power decreasing?

One answer is that the Republicans in Congress have refused to compromise.

For other opinions, check these sites.

http://www.google.com/#hl=en&sa=X&ei=3J-lT6OdG9Luggf8gqTRAQ&sqi=2&ved=0CBwQvwUoAQ&q=u.s.+presidential+power+decreasing&spell=1&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=d0f8cd49a0fc8cd2&biw=711&bih=453