Political scientists have long theorized about why senators and representatives decide to vote a particular way on a piece of legislation. While there is no hard-and-fast rule that governs the decision-making process, there are several considerations that most members factor into the equation.
A majority of the votes that take place in Congress occur along straight party lines, meaning that an overwhelming number of Republicans vote one way, and a majority of Democrats the other way. This should come as no surprise, considering that the primary function of Congressional leaders and whips is to enforce party discipline during votes. As a result, party affiliation is the best indicator of a member's vote.
In some cases, members will take into account the views of their constituents. This is especially true if it's a high-profile or polarizing issue such as gun control, abortion, tax cuts, or sending troops abroad. It's not unusual for members to vote against their own beliefs if they're in conflict with their constituents' viewpoints.
However, sometimes the opposite occurs, as was the case with Democratic Representative Marjorie Margolies-Mezvinsky, who represented a swing district in Pennsylvania. Margolies-Mezvinsky cast the deciding vote in favor of President Clinton's 1994 budget plan (which increased taxes), and was subsequently voted out of office by her conservative constituents.
Although members of Congress pride themselves on their independence from the executive branch, presidential persuasion weighs heavily on key Congressional votes. Historically, when the president has an announced position on an issue, he prevails on about 75 percent of the Congressional votes. Leading up to the 2002 midterm elections, many southern and midwestern Democrats facing re-election voted for President George W. Bush's agenda at the “behest” of the White House, even though the party leadership was opposed to his agenda.
As a general rule, the more popular the president, the more “persuadable” the Congress. President Lyndon Johnson was particularly adept at using presidential pressure (some would call it arm-twisting) to gain support from Congressional Democrats for his Great Society programs, civil rights initiative, and the war in Vietnam. Johnson had mastered the art of “subtle persuasion” while serving as majority leader of the Senate.
Sometimes lawmakers will strike deals with other members to cast a vote a certain way in return for the same consideration on a future vote. Most vote trading takes place on low-profile and procedural matters — it rarely occurs on highly public issues. Vote trading is particularly common when a member is trying to take a spending project back to his or her district.
What is logrolling?
Logrolling is the process of vote trading as it relates to omnibus pork-barrel spending projects. This occurs when narrow interest groups band together on public works, subsidy, tariff and trade, or taxation legislation so that each constituency gets something from the bill. Participating members will then vote for the entire package, regardless of the provisions, as long as their narrow interest is included.
In the rarest of cases, members will vote according to deeply held ideological or philosophical beliefs about the role of government. Sometimes ideological voting is consistent with straight party voting. At other times, depending on the issue, ideological voting splits across party lines. This often is the case with First Amendment, abortion, and gun control legislation.