McConnell has been widely described as an obstructionist. As the leading Republican senator, McConnell confronted and pressured other Republican senators who were willing to negotiate with Democrats and the Obama administration. According to Purdue University political scientist Bert A. Rockman, "pure party line voting has been evident now for some time . . . but rarely has the tactic of "oppositionism" been so boldly stated as McConnell did. " According to University of Texas legal scholar Sanford Levinson, McConnell learned that obstruction and Republican unity were the optimal ways to ensure Republican gains in upcoming elections after he observed how Democratic cooperation with the Bush administration on No Child Left Behind and Medicare Part D helped Bush's 2004 re-election. Levinson noted, "McConnell altogether rationally. . . concluded that Republicans have nothing to gain, as a political party, from collaborating in anything that the president could then claim as an achievement. " A number of political scientists, historians, and legal scholars have characterized McConnell's obstructionism and constitutional hardball as contributors to democratic erosion in the United States.