Last month we celebrated the birthdays of George Washington and Abraham Lincoln, two presidents whose deep but somewhat unconventional faith has evoked great debate. Does the faith of presidents truly matter? Does it significantly affect how they think, live, and govern?  Concluding that it does not, most biographers have treated presidents’ religious convictions as no more important than hobbies such as collecting stamps or playing golf. Many other Americans, however, have considered the faith of presidents as either a cause for celebration or alarm. While Christians often campaigned vigorously and voted in droves for candidates who shared their faith, their foes warned that the dangerous religious views of other presidential aspirants made them unacceptable for the nation’s highest office.

In the presidential campaign of 1800, Federalists denounced Thomas Jefferson as an infidel who would subvert the nation’s Christian foundation. Rumors spread that, if elected, Jefferson would use public funds to entice civil servants, teachers, military officers, and even ministers to either ignore religion or teach secularism. After Jefferson won, these claims prompted many Federalists in New England to bury their Bibles in their gardens so that his administration could not destroy them.

In 1908, Theodore Roosevelt assured apprehensive prospective voters that William Taft’s Unitarian faith did not disqualify him from being president. Twenty years later, fundamentalist Protestants argued that Democratic candidate Al Smith’s Catholicism made him unfit to be president. Despite John F. Kennedy’s assurances that he would be guided by the Constitution and his conscience, not the pope, his Catholic faith was as controversial in 1960 as Smith’s had been in 1928.

Jimmy Carter’s affirmation that he was born again baffled and frightened many Americans as did George’s W. Bush’s assertion that Jesus was his favorite philosopher. Many worried that their decisions would be based on what they perceived God wanted them to do rather than on the advice of their cabinet and the nation’s strategic needs.

Are these concerns justified? Does the faith of presidents truly affect how they govern?  Does it help shape their perspectives, policies, actions, and decisions?  The answer depends on which chief executives we are discussing. The faith of some presidents (such as Kennedy ironically) mattered little. The faith of many others, including Hoover, Carter, Bush, and surprisingly Jefferson, strongly influenced their political philosophy and policies.

Although it is impossible to disentangle the personal religious convictions of presidents from their use of religion to serve partisan political purposes, many of them were more deeply religious and had more vibrant personal devotional lives than most scholars have recognized. Presidents use religious language and engage in religious practices to win public approval and gain political advantages. Therefore, we must judge whether their faith is authentic by examining their private correspondence as well as their public pronouncements and evaluating the testimonies of those who knew them best. We must also assess their statements and behavior before, during, and after their presidencies.

Their religious practices – frequent church attendance, prayer, and reading of the Bible – close relationships with some religious groups, regular use of religious rhetoric, and particular policies all testify that their faith was important to many chief executives. Most presidents have worshipped consistently to continue their life-long practice, seek divine guidance, set a good example, or to please prospective voters. Almost all presidents have extensively used moral and biblical language to console grieving Americans, provide assurance in times of crisis, celebrate religious holidays, and promote particular policies.

The faith of many presidents has also helped shape their policies and determine their decisions. Numerous other factors – strategic considerations, national security, party platform commitments, campaign promises, political philosophy, relationships, and reelection concerns – affect their decisions. Nevertheless, their religious commitments have strongly affected the policies many presidents adopted. Religious beliefs helped inspire George Washington’s quest to guarantee religious liberty, Jefferson’s to ensure peace, and Abraham Lincoln’s to end slavery. Their Christian convictions helped prompt William McKinley to declare war against Spain and take control of the Philippines, Theodore Roosevelt to establish national parks, Woodrow Wilson to devise the Treaty of Versailles, Herbert Hoover to reform prisons, and Franklin Roosevelt to remedy the ills of the Great Depression. Harry Truman’s decision to recognize Israel, Dwight Eisenhower’s attempt to reduce armaments, Carter’s quest to promote human rights, Ronald Reagan’s crusade to crush communism, Bill Clinton’s efforts to resolve international conflicts, George W. Bush’s support for faith-based initiatives, and Barack Obama’s policies on poverty were all motivated in large part by their faith.

Has the faith of presidents affected them and their administrations positively or negatively?  The answer to this question depends largely on how individuals view the religious convictions and policies of particular presidents. However, when people’s faith gives them confidence, assurance, comfort, and inspiration, it is generally beneficial. People’s faith often stimulates them to be more compassionate, generous, and hopeful and supplies a constructive blueprint for bettering society. Moreover, the faith of presidents has often greatly aided them in carrying out their demanding duties and serving as the nation’s pastor-in-chief during crises and calamities.

Faith has played a very important and often controversial role in the lives of American presidents from George Washington to Barack Obama. Although the founders wisely separated church and state, religious belief and politics have often been inextricably joined and will undoubtedly continue to be.

Gary Scott Smith is a fellow for Faith and Politics at the Center for Vision and Values. He is the author of Faith and the Presidency: From George Washington to George W. Bush (Oxford University Press, 2006) and Religion in the Oval Office: The Religious Lives of American Presidents (Oxford University Press, 2015).