Which is one reason why the power and responsibility of the president has increased?

The presidency is often called "the most powerful office in the world," and it is! But what makes it so powerful? Article II of the Constitution gives the President power to command the armed forces, make treaties, send or receive diplomats, approve or veto acts of Congress and take care that laws be faithfully executed. 

Presidential power has grown significantly over time.  One main reason for this is because as the role of the federal government has grown and the country has endured wars and other major crises, citizens have looked to the presidency for leadership. Congress has also delegated authority to the executive branch to carry out laws, which has in turn given the President more power.  Another reason for growth of presidential power is that the size of the staff supporting the President has grown, which has allowed involvement in more areas of government to grow.  The media also plays a major role in presidential power growth, since the media shows people what is going on in the presidential office. 

Even with the increase of authority, the Constitution says that no President can become all-powerful.  For example, in 2006, George W. Bush planned to use military tribunals to prosecute enemy combatants, but the court found that his decision violated the Constitution.