By Bob Benenson, CQ Staff

CQ Politics Editor Bob Benenson offers a quick course in Primaries 101.

1. What is the difference between a primary and a caucus?

A primary is a candidate-nominating event virtually identical to a general election. Participants go to polling places or mark absentee ballots to vote for the candidates they favor as party nominees for the general elections.

A caucus is more like a town meeting or a party convention. While exact practices vary from state to state, most caucuses feature pitches on behalf of the candidates, followed by votes that can range from secret ballots to a show of hands to supporters of individual candidates actually gathering together in separate parts of the caucus room.

In either case, delegates are allocated among the candidates based on their shares of the total vote. Democratic presidential candidates in all states must meet a 15 percent threshold to qualify for delegates; most state Republican Party organizations have a similar threshold.

2. What is the difference between ‘open’ and ‘closed’ ?

A “closed” primary or caucus is one in which only voters registered with a party can participate in its nominating events.

An “open” primary or caucus is one in which all voters, regardless of party affiliation or lack thereof, can participate.

Completely open primaries in states with party registration are rare, as court rulings have found that they allow non-party members to influence decisions and therefore violate members’ freedom of association. But other states have no party registration, so their primaries and caucuses are open to all comers.

The “modified open” primary or caucus is usually defined as a contest that also is open to participation by independent (also known as unaffiliated) voters.

3. How are presidential primaries scheduled?

Cynics would say “Haphazardly.” The real answer is that the individual states and, at times, the individual parties within the states (see number 5 below) set the dates for their own primaries.

This was not a big deal during the early era of presidential primaries, which ran from 1912 through the 1968 campaign. The presidential nominating process in most states conducted in caucuses dominated by party insiders, and the handful of primaries each election year was strung out over the course of several months (usually beginning in early March and ending in late June).

But reforms aimed at opening the nominating process to more voter participation, first instituted for the 1972 campaign, led to a proliferation of primaries. This produced “front-loading,” as many states moved their contests earlier in the year to try to compete with the established first-in-the nation Iowa caucuses and New Hampshire primary.

While there are proposals to more evenly distribute the nominating contests across the first half of the presidential election year, none has been instituted.

4. Why do some states have different dates for different parties’ presidential primaries?

States that use taxpayer money to finance party primary elections almost always hold the contests for both major parties’ nominations on the same day, for the convenience of voters and also to save money. But in a few states, the parties pay to conduct their own primaries and are at liberty to schedule them whenever they want. For example, South Carolina Republicans have their presidential primary on Jan. 19, while the Democrats go to the polls on Jan. 26.

5. How do delegates factor into the actual nomination?

Delegates at the parties’ national convention long played a significant role in determining their party’s nominee, since only a small portion of the delegate votes were apportioned on the basis of primaries. But the proliferation of primaries since 1972 has made them the dominant means of meting out delegates – with the result that the front-running Democratic and Republican candidates have been able to garner majorities of the convention delegates and clinch their nominations during the primary season.

This has greatly diminished the functional role of individual delegates, who over recent election years have often been described as little more than “extras” in the four-day televised party “infomercials” that many say conventions have become. Yet the possibility always exists that a presidential nominating contest will deadlock among several candidates and then none will achieve a majority, putting the ultimate decision into the hands of the delegates.

6. What do the different delegate classifications mean?

There are different classifications for delegates to the national conventions:

• Pledged delegates: These are delegates required under the rules of both major parties to support the candidates to whom they have pledged their support - at least on the first ballot at the national nominating conventions. All but a small fraction of Republican delegates go to the convention as pledged, and a sizable majority of Democratic delegates do as well. Candidates who won delegates early on and later dropped out often waive this requirement, though.

• PLEOs (Party Leaders and Elected Officials): This designation, which applies only to Democrats, was created to ensure that party officials and officeholders maintain a significant role in the nominating process. While about a third of the PLEOs go to the convention officially pledged to a presidential candidate, the rest are designated as unpledged superdelegates. Since 1984, the Democratic Party has set aside an officially unpledged portion of its delegate slots for party officials and officeholders. The idea behind this, developed in the wake of President Jimmy Carter’s one-sided defeat by Republican Ronald Reagan in 1980, was to give party officials a chance to perhaps shift their weight behind another candidate deemed more “electable.” But since then, a single dominant candidate has clinched the requisite delegate majority well before the convention. So, most PLEOs have typically fallen into line and endorsed the people’s choice. For the 2008 convention, superdelegates will make up just less than 20 percent of all delegates.

• District-level and at-large delegates: The parties divide their pledged delegates into two groups. District-level delegates are those chosen at the congressional district level. At-large delegates are chosen on a statewide basis, in some states at the state party convention and in slates drawn up by the candidates’ campaign organizations.

7. How are congressional primaries scheduled?

States set their own schedules for congressional primaries. This date is typically inscribed in state election law, and most states have long held to a traditional date at some point between early March and mid-September. In presidential election years, though, several states pair their congressional primaries with their presidential primaries.