When Barack Obama and John McCain accept their party's presidential nominations at raucous, overflowing convention arenas in Denver and St. Paul, the 20 million or so viewers watching on television may be forgiven for assuming they are witnessing an actual news-making event.

Instead, they will be watching one of two $40 million productions designed to highlight a single political narrative with the perfect visuals and the perfect audience, and, for just a moment, to show off the perfect candidate.

In truth, conventions over the past 20 years have become wild parties for delegates, activists and top donors, but they weren't always newsless excuses to press the flesh, drink too much and wear silly hats amid streamers and confetti as something we already know (That McCain and Obama become their party's nominees) becomes official. Over the 175-year history of presidential nominating conventions, some actually mattered; the closely-guarded secret both parties don't want to be known is that their conventions this year will be more important than normal as well.

Baltimore, Maryland, residents claim the Anti-Masonic Party held the first convention in their city to choose their nominee in 1831, while Democrats followed suit in the same city in advance of the 1832 campaign. Republicans held their first nominating convention in 1856, four years before nominating a former member of Congress, Abraham Lincoln.

That Obama and McCain will stand alone as their party's most obvious nominees is a change unto itself. Lincoln stood alongside four other party stalwarts, including former Ohio Governor Salmon P. Chase and New York Senator William Seward (Both would play roles in Lincoln's administration, Chase as Treasury Secretary and Seward as Secretary of State, during which time he committed "Seward's Folly," purchasing Alaska for about two cents per acre).

Today, the roll-call votes both parties hold is a spectacle. The delegation chairman, be it a party elder, a member of Congress or a governor, will step to the microphone and declare their state's votes for their party's nominee, while cameras focus on a delegate with a particularly moving story or a particularly outrageous costume. In the end, it is likely that both candidates will be nominated "by acclamation," a parliamentary move designed to showcase unity of purpose.

In St. Paul, McCain will secure the votes of a majority of convention delegates on the first ballot (All but a handful of delegates who back Texas Rep. Ron Paul are expected to support McCain). The same goes for Obama in Denver, though he will acknowledge the tough primary from which he emerged by allowing backers of Hillary Clinton to vote for their candidate as well.

But for Lincoln, things weren't so easy. The Republican convention, held that year in Chicago, required three ballots to give Lincoln a majority. Taking three ballots weren't anything special; in 1924, thanks to a feud between New York Governor Al Smith and those who opposed nominating a Catholic for president led by former Treasury Secretary William McAdoo, former ambassador to Great Britain John W.

Davis became the compromise Democratic nominee after an incredible 103 ballots.

Perhaps the most dramatic change in convention history has been the influence of ordinary voters throughout the country, rather than tight control by party bosses. Democrats opened their nominating process to caucuses and primaries that elect delegates after the disastrous riots of 1968, when party elders selected Vice President Hubert Humphrey as their standard-bearer even though he never won a single primary.

Following the riots in Chicago, a party commission headed by Senator George McGovern instituted a system by which results of caucuses and primaries in each state would determine how delegates to national conventions were allocated. McGovern also allowed one state, Iowa, to hold their caucuses first, the origin of the Hawkeye State's claim to historical precedent; when he decided to run himself in 1972, McGovern's campaign focused attention on Iowa and vaulted to front-runner status after winning the first-in-the-nation contest, eventually capturing the nomination.

Today, delegates allocated by those caucuses and primaries are making their way to Denver and St. Paul to cast their ballots. Both parties have gone to extraordinary lengths to ensure that each convention is a picture of party loyalty – the last seriously contested conventions came in 1976 for Republicans, when former California Governor Ronald Reagan came within 117 votes of beating President Gerald Ford, and in 1980 for Democrats, when Ted Kennedy ran a spirited but losing campaign to best President Jimmy Carter.

Finally, considerations for both parties have changed considerably as well. Lincoln's convention in Chicago was more about consolidating votes and making grand speeches to woo new delegates than any appeal to the media. Today, the media spectacle determines which candidate gets the biggest so-called "bounce," or boost in poll numbers in the days following a convention, and a phenomenon about which no pollster can seem to agree, even as to whether it really exists.

Adding new wrinkles are new technologies that will allow voters to see even more of the convention. Both parties are investing heavily in internet campaigns that will go behind the scenes and purport to draw back the curtain on the convention's inner workings.

Also this year, for the first time, both candidates' personal blemishes will be most on display, as viewers tuning in on high-definition televisions will get to see every line, mole and pore on both faces. Candidates will prepare for their time in the spotlight with makeup made for high-definition, which comes in the form of a fine mist instead of the traditional caked-on method.

But behind the scenes this year, party loyalty is being tested on both sides. Backers of Hillary Clinton are demanding their due in Denver, threatening to disrupt the convention so much that Clinton's aides have formed rapid-response teams to shut down any anti-Obama backlash from her supporters.

And while most polls show the vast majority of Clinton voters backing Obama, the party still has some squeaky wheels who could make noise at the convention, both inside and outside, in full view of a media hungry to pursue the story.

Well in advance of the Republican convention, conservative activists are doing their best to influence the party's platform. The committee which will adopt the document, chaired by freshman California Rep.

Kevin McCarthy, has a number of conservatives as members, many of whom do not see McCain as an ally on issues of concern. A heavy focus on abortion restrictions, bans on same-sex marriage or other social issues – positions McCain has agreed with throughout his career but has been reluctant to make a centerpiece of his campaign – could be embarrassing to the nominee.

Also, members of both parties are doing their best to once again alter the manner in which nominees are selected.

Democrats, who earlier this year underwent the spectacle of stripping Michigan and Florida of their convention delegates before reinstating half their voting powers, will deal with the perceived harshness of those penalties, as well as the role so-called superdelegates – members of Congress, governors and party leaders – play in the process.

Republicans, meanwhile, have much more strict guidelines regarding calendar violators, and the 2012 primary schedule will be set at the St. Paul convention, under party rules. Factions within the Republican National Committee are working to find a new calendar that states would find fair.

Still, the latest plan that seemed to gain traction has all but died, say those involved in calendar negotiations. Making situations even more complicated, Iowa and New Hampshire, which claim the historical mandate to go first, refuse to gi
ve up their spots at the front of the pack.

Though they will cover it obsessively and interview every delegate on whom they can get their hands, network and print media will remind viewers and readers repeatedly that coronations of John McCain and Barack Obama are little more than show, and that nothing unexpected will happen. Throughout history, they have a point; neither candidate will take 103 ballots to be nominated, and the vice presidential candidate won't even get a roll call – he or she will be elected by voice vote.

But on deeper levels, both conventions do matter, not only from the visuals they will send to the millions of viewers who tune in to watch but to the future of both parties. The two most important legacies both conventions will establish will be the most public, the presentation of candidates' narratives to the electorate, and the most private, the establishment of rules and procedure. The first could determine whether Barack Obama or John McCain wins in November; the second could determine who serves as president in 2012 and beyond.