Americans will have the opportunity this evening to watch President Barack Obama and Republican presidential nominee Mitt Romney debate. It will be the first of three presidential debates this election season.

The vice presidential candidates, Vice President Joe Biden and Congressman Paul Ryan, will have a single opportunity to debate on Oct. 11 at Centre College in Danville, Kentucky.

The first televised debate between the two major party presidential nominees occurred in 1960 between John F. Kennedy and Richard Nixon. And while Professor Larry Sabato of the University of Virginia says that presidential debates seldom make a difference in election outcomes, many observers believe that this first debate did play a significant role in the election of Kennedy to the White House. Nixon had just spent two weeks hospitalized for an infection. During his debate, Nixon looked very pale and sickly in comparison to the young, tanned Kennedy.

After this first debate, Americans would have to wait until 1976 to watch another. Then, President Gerald Ford and Georgia Gov. Jimmy Carter debated. This meeting was the first to be sponsored by the League of Women voters, a non-partisan group which went on to sponsor the presidential debates in 1980 and 1984.

In 1988, however, the two major parties started exerting more control over the format and rules of the debates to the point where the League withdrew as a sponsor because it did not want to give its name to the debates which were, in their words, "controlled and scripted by the candidates' campaign organizations." As a result, the Commission on Presidential Debates was formed by both major parties.

In 1992 Ross Perot was the first third-party candidate to participate in a presidential debate. This participation significantly influenced his campaign. Perot was polling at around 7 percent before his debate performance, but secured 19 percent of the vote in the election. He was excluded, however, from the 1996 debates.

In response to questions regarding the participation of third party candidates in televised debates, in 2000 the Commission on Presidential Debates announced a 15 percent polling threshold for candidates to participate. Since Perot, no third-party candidate has reached this threshold, and debates have been limited to the two major party candidates.

The format of the debates has ranged from three-member panels to a single journalist asking questions. This year, questions will be asked by a single moderator selected and agreed upon by both candidates.

Some believe that the format of the modern presidential debate is so structured and controlled by the candidates that a true debate is impossible. Of course, both parties want this structure to protect their candidate.

Tonight's debate will focus on domestic policy. It will be moderated by Jim Lehrer, the host of News Hour on PBS, and held at the University of Denver in Colorado. A second presidential debate will be held on Oct. 16, followed by a final meeting on Oct. 22.

Presidential debates still receive good television ratings. Then again, viewers don't have much of a choice as the debates are usually broadcast on most channels. However, over the last four decades, the number of American households watching the presidential debates on television has declined from about one in three in 1980 to just over one in five in 2008. Of course, a growing number of folks are following the debates online rather than on the television.

Regardless of how you follow this evening's debate, I hope you enjoy the show.