As president of the Senate, Vice President Dick Cheney welcomes returning senators, including Sen. Hillary Clinton (and husband, former President Bill Clinton), during the swearing-in ceremony of the 110th Congress in 2007.

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The Vice President as President of the Senate

The office of the vice president of the United States is a unique one. It's the only office in the federal government that straddles two of the three branches of government, the legislative and the executive. Since the vice president serves as an official of the executive branch but also as the president of the Senate, some in the course of history have found the office an affront to the separation of powers [source: Hatfield]. Customarily, however, vice presidents have chosen to focus on either the legislative or the executive duties, rather than both.

­The vice president's presiding powers over the Senate are largely hamstrung by the strict rules order the Senate adopted centuries ago. During the leisure time afforded during his vice presidency, Thomas Jefferson wrote a procedural handbook that the Senate and the House still use as a guide today.

While in the Senate, the vice president is expected to speak only when ruling on an issue of order, and in another case, when carrying out the Senate president's official duty of announcing the electoral tallies for the presidential race. This has proven sticky for some vice presidents who've run for the presidential office and lost; they were forced to announce to the Senate the victory of their rivals. Four vice presidents -- John Adams, Thomas Jefferson, Martin Van Buren and George H.W. Bush -- had the satisfaction of announcing their own victories to the Senate [source: Hatfield].

The vice president's main power is the ability to cast the tie-breaking vote in the Senate. This isn't as powerful as it sounds. Senate leaders commonly lobby for support for a bill before they call for a vote on the Senate floor. So senators know ahead of time whether a bill has enough votes to pass. What's more, the Senate president's vote only counts if the vote is affirmative; essentially the vice president can only vote yes. That's due to Senate procedural rules that state a bill has been defeated if a tie is reached. The only effect a vice president can have in a tie breaker is if he or she votes yes to break a tie, since a no vote on an already defeated bill is useless.

Some vice presidents have taken their role as president of the Senate seriously. Thomas Jefferson saw the role as the sole one he had as vice president and stayed in Washington only when the Senate was in session. (Jefferson saw his election to the vice presidency in 1796 as a chance to rest up and await the presidency in the next election.) Vice President Spiro Agnew, who served under Richard Nixon, spent time in the Senate, but vacated the responsibility after one senator accused him of lobbying on the Senate floor, which is illegal. Vacating the presidency of the Senate is a long-held tradition among most vice presidents. According to Senate procedure, a temporary president (a serving senator) can only be chosen in the absence of the vice president. So the vice president simply leaves the Senate chambers and the Senate chooses a president pro tempore.

Find out about the support and staff the vice president enjoys on the next page.