(CNN) -- U.S. political parties' conventions are relics. They don't decide the nominees any more. That's been turned over to primary voters. And no one pays much attention to party platforms except a few ideological activists.
Obama first hit the national political scene during the Democratic 2004 convention.
So why do we still have them? Two reasons: money and publicity.
Parties can raise big money at conventions. Major contributors are treated to endless receptions and special events. The actual convention business -- nominations, acceptance speeches, platforms (party programs) -- easily could be completed in a weekend.
But the process is stretched out over four days to provide plenty of time for fundraising.
The convention has evolved into a four-day "infomercial," a slick production aimed at promoting the candidate and giving the ticket a "bounce" in the polls.
It wasn't always like that. In 1972, it was sensational news when the press discovered a detailed, minute-by-minute script for the Republican convention.
The Democrats had no such script and it showed. The 1972 Democratic convention was far more "democratic" -- and chaotic. The nominee ended up giving his acceptance speech in the middle of the night after days of infighting, with disastrous results.
Despite a bitter convention battle, George McGovern was nominated and went on to lose by one of the biggest margins ever.
Now both parties try to control every minute of the convention as if it were a television show. Because it is a television show.
Delegates are props. They cheer and applaud and provide "color" (funny hats). The last thing convention organizers want is actual news made. But somehow news usually manages to break out.
Think of it this way. At the Democratic convention in Denver, Colorado, a little more than 2,000 delegates for Sen. Barack Obama and a little under 2,000 delegates for Sen. Hillary Clinton will be meeting in one big room. Singing "Kum Ba Ya"? Not likely. They'll find plenty of things to squabble over.
Obama plans to deliver his acceptance speech in a stadium with 76,000 seats instead of the conventional hall. Here's one reason: An audience of 74,000 Obama fans will swamp 2,000 Clinton delegates.
Republicans have two big worries for their convention. One is what to do with President Bush and Vice President Dick Cheney -- two of the most unpopular figures in U.S. politics.
Bush and Cheney have to be given time to say farewell to their party. When they do, Sen. John McCain wants to be far away. Otherwise, he would be expected to raise arms with Bush and Cheney -- and provide a photo that would live forever in Democratic campaign propaganda.
Conservative activists are determined to write a party platform that limits McCain's influence. Meaning, no stem cell research. No global warming. No campaign finance reform. No comprehensive immigration reform. Convention organizers want to make sure the platform process, like the Bush and Cheney speeches, gets as little notice as possible.
Nevertheless, if you look beyond the hoopla and the bombast at the conventions, a real story will be going on. It is about the remaking of the Democratic and Republican parties.
The Democratic Party has been the Clinton party for 16 years. Now the Obama campaign wants to remake it into the Obama party.
The process started just after Obama claimed the nomination. He moved major party operations from Washington to Chicago, Illinois, where his campaign is headquartered. He ordered the party to stop accepting contributions from groups that lobby the federal government.
In the United States, political parties are diverse coalitions united by one thing: the desire to get the party's candidates elected.
Coalitions are held together by calculation and strategy. The Clintons were extremely good at calculation and strategy. Remember "triangulation" -- President Clinton's technique of splitting the difference with people on both sides of an issue? And the Clintons were winners. Until this year.
This year, Hillary Clinton was defeated by something the Clintons didn't see coming -- a political movement.
A movement is held together by more than calculation and strategy. A movement is based on belief and belonging. People support a campaign. But they belong to a movement. Movements can be difficult to elect. They alienate "nonbelievers" who don't feel they "belong."
The Democratic convention will be the first formal meeting of the national Obama movement. We'll be watching to see how the Obama campaign tries to reshape the party's image and message. And whether the Clinton delegates put up resistance.
Precisely the opposite will be happening at the Republican convention.
The Republican Party was captured by the conservative movement when Ronald Reagan won the nomination in 1980. The conservative movement nominated George W. Bush and rejected McCain in 2000.
Now the McCain campaign wants to remake it from a Bush party to a McCain party. That means limiting the influence of movement conservatives who have controlled the party for nearly 30 years.
McCain wants the Republican Party to be a party of reform, not just conservatism. That way he can look like a candidate of change instead of a third term for Bush. That's a calculation and a strategy. It's also a challenge to conservatives.
McCain will try to remake the Republican Party in his image, and conservatives may resist. That will provide much of the drama -- and the news -- at the Republican convention in Minneapolis-St. Paul, Minnesota.