eliminating the ability of the president to fully disrupt the government, and further strengthening the prime minister's position. Under President Aleksander Kwaśniewski, Prime Minister Jerzy Buzek's government became the first administration to be elected under the new constitution. Despite being from opposite parties (Kwaśniewski's center-left Social Democracy of the Republic of Poland and Buzek's center-right Solidarity Electoral Action), the relationship between both offices was smooth, partly due to Kwaśniewski's non-confrontational personality. Kwaśniewski sparingly used his veto powers in legislation the president did not agree with, choosing to let the government's concordat with the Holy See, a new lustration act and new electoral statutes to proceed without hindrance, though Kwaśniewski vetoed Buzek's privatization plan. Kwaśniewski's relationships with the like-minded social democratic premierships of Leszek Miller and Marek Belka were virtually free of conflict. Relations between the two executive organs, however, returned to animosity under the presidency of Lech Kaczyński and Prime Minister Donald Tusk. Political rivals for years, fueled by the 2005 presidential poll which saw both men as the main challengers, Tusk's center-right Civic Platform toppled President Kaczyński's twin brother Jarosław's government in the 2007 parliamentary election. Tusk's support for stronger integration into the European Union, including the signing of the Lisbon Treaty, and a rapprochement with Russia, put Kaczyński directly at odds with the prime minister. From 2007 until Kaczyński's death in the Smolensk air disaster in 2010, policy differences between the two offices were a constant source of division, with the president employing his limited veto powers numerous times over the government's legislation; Tusk's government lacked a 60 percent threshold to overturn such vetoes. In response, Tusk made no secret his party's desire to replace Kaczyński in the 2010 presidential election. Although Tusk and Kaczyński found several areas of compromise, clashes between the Chancellery and the Presidential Palace became a regular feature in both the domestic and international political scenes for the next two and a half years. Frustrated by Kaczyński's veto, Prime Minister Tusk argued for a constitutional amendment in November 2009 to strip the presidency of its veto powers, declaring: "The president should not have veto power. People make their decision in elections and then state institutions should not be in conflict...Let us change some provisions so we can have fewer conflicts and more cooperation. We propose changes to the constitution so that the centre of power lies with the government... The presidential veto brings more