Chuck Baldwin has learned that America is a place any boy can grow up to be president so long as he's a Democrat or a Republican.

A Baptist minister and talk show host, Mr. Baldwin is the presidential candidate of the Constitution Party, and, like candidates before him from Ross Perot to Ralph Nader, he has run through the hall of mirrors that makes up the election laws of the 50 states.

Some require hundreds of thousands of signatures to get on the same ballot where spots are reserved for the major parties. Others require a handful of signatures and a bit of paperwork. Some lay out rules so intricate that third parties spend most of their state budgets just landing a ballot position and then defending it in court against challenges.

"It's extremely difficult for third parties to get on the ballot," Mr. Baldwin said. "It's purposeful in my opinion."

Bob Barr, the Libertarian candidate -- who made the Pennsylvania ballot -- feels much the same as his exiled compatriot.

"This is just another illustration of how the two major parties stack the deck against anybody daring to play on their playing field," he said.

Mr. Barr took his campaign to Pittsburgh as the weekend began, speaking before students and supporters at Carnegie Mellon University. Two weeks earlier, Ralph Nader, a man driven from the ballot four years ago in what the state attorney general is now characterizing as a criminal conspiracy, gave his pitch to an enthusiastic crowd at the University of Pittsburgh.

Often referred to as a spoiler who drew votes from Democrat Al Gore in Florida in 2000, effectively handing the state to George W. Bush, Mr. Nader nearly erupts with indignation when asked if he should be running or if he should possibly endorse one of the two party candidates.

During a question-answer session at Pitt, Mr. Nader snapped back at a woman who asked him if he might consider endorsing one of the two major party candidates as a way of having an effect on the race.

"You're treating me like a second-class citizen," he said. "You would never ask that question if Obama or McCain were here. We have to break the grip of the two party system. It is corrupt, it is not responding to the necessities of the American people and hasn't for decades."

The grip of the two parties, as laid out in disparate state election laws, is fairly clear to men like Mr. Nader and Mr. Barr.

In Oklahoma, for instance, where ballot access is among the most restrictive in the nation, neither Mr. Barr nor Mr. Baldwin nor Mr. Nader found a place on the ballot.

Perhaps nowhere is the design to exclude more transparent than in Pennsylvania, a state that once was among the more open to third parties. A series of changes in Pennsylvania's election laws, starting in 1971 and running through the 1980s, forced third parties and independent candidates to spend increasing amounts of time and resources just to attain a ballot spot. The effect is visible.

Mr. Baldwin was unable to muster the needed signatures to reach the state's ballot, despite being endorsed by Rep. Ron Paul of Texas, a libertarian Republican who attracted widespread national support. His supporters, many of whom worked for Mr. Paul in the early days of the campaign, were simply worn out.

"After a party ages a little bit its activists just get sick and tired of petitioning," said Richard Winger, a California-based expert on ballot access and third parties. "They just can't keep it up. It's drudgery. You just cannot sustain it. So these parties get tired and give up."

Until 1971 in Pennsylvania, an 1891 law required minor parties to scrounge up voter signatures equal to one-half of 1 percent of the highest vote total in the preceding general election.

Third parties from the far right to the Communists shared a spot -- if rarely an elected office -- alongside the Democrats and Republicans. The Consumer Party, largely a Philadelphia phenomenon, had its own primaries. The Prohibition Party had its own primary until the 1930s, as did the Socialists.

All in all, third parties enjoyed a regular place in Pennsylvania politics through the 1960s.

In 1971, without explanation, the number of signatures required to get on the ballot was quadrupled to 2 percent.

Third parties went to court the following year and a court upheld the higher signature numbers but struck down the part of the law that gave them only three weeks to gather those signatures.

Unchanged, for the time being, was the part of the law that entitled any party that gathered 2 percent of the highest vote-getter's numbers to its own primaries.

That changed when the Democratic Primary saw a crowded ballot 30 years ago. The Legislature moved to increase the number of signatures needed to get on a primary ballot, doubling the number of signatures needed to get on the ballot for Senate and bumping the number needed for a statewide office from 100 signatures in each of five counties, to 100 in each of 10.

That would work for the Democrats and Republicans, but for the Consumer Party, which had only 7,000 members statewide, the chances of two candidates coming up with enough signatures in various counties looked dim.

They went to court.

In federal court, Judge Norma Shapiro ruled that the smaller parties would have to lose their primaries. They won on appeal and Judge Shapiro took the unusual step of writing to the general assembly warning them of potential chaos.

The legislature took all of two days to pass a law that ultimately created a series of classes for various parties by declaring that in order for a party to qualify for a primary it must have at least 15 percent of the state's registered voters.

At the top, called "major parties," were the Democrats and Republicans. "Minor Parties" were those that got 2 percent of the vote total statewide and 2 percent of the highest vote for a statewide candidate in each of 10 counties. Below that were "political bodies," essentially parties that hadn't gotten enough votes in a preceding election to meet any of the other standards.

Were the Pennsylvania laws applied to Massachusetts, the Republicans would not qualify as a major party there. Their candidates would have to gather tens of thousands of signatures to get on the November ballot. In Utah, the Democrats would be in the same fix.

Other states have their own hurdles. In 1943, Georgia's legislature raised the signature requirement for a third party candidate so high that no third party has fielded a candidate for the U.S. House in a regular election since then.

By contrast, Vermont grants automatic ballot status to any party that has organized in 10 towns. By organization, that means a chairman and a secretary. Essentially, a 20-member organization can find a spot for its candidates on the Vermont ballot, said Mr. Winger.

Pennsylvania is among a handful of states in which individuals can seek to have a nominee's petitions thrown out. In 2004, using state-paid workers in a scheme uncovered as part of the investigation into the state payroll bonus scandal, the Democrats successfully pushed Mr. Nader off the ballot by claiming widespread fraud and forgery in his petitions.

Two years later, the Democrats did the same thing to Carl Romanelli, the Green Party candidate for U.S. Senate, whom they feared would siphon votes from Democrat Bob Casey.

Caught in the crossfire of that one was Titus North, a University of Pittsburgh professor who ran for Congress against incumbent Democrat Mike Doyle in the 14th District.

Mr. North had collected ballot signatures for the Green slate, which included Mr. Romanelli. As such, he found himself defending the validity of signatures, including personal friends he had seen sign his petition.

With Democrats providing manpower and a Pittsburgh law firm overseeing the effort, Mr. North said he was worn down physically.

"It was four full working weeks to be down in Harrisburg every working day," Mr. North said. In the evenings, he would dash out of the office in Harrisburg and drive 220 miles west to teach his Pitt classes.

At one point, he said, an attorney for the Democrats pointedly informed him that he could be held accountable for court costs if he lost -- a decision the state courts handed down against Mr. Nader, demanding he pay $81,000 to Reed Smith, the law firm that represented the Democrats in the 2004 petition challenge.

"I couldn't afford that," said Mr. North, who ultimately won and remained on the ballot -- the only challenger to Mr. Doyle.

This year, Mr. North will again challenge Mr. Doyle. On the presidential ballot, voters can choose from among the Democrats, the Republicans, Mr. Nader, and Mr. Barr.

For Mr. Baldwin, whose forces couldn't muster the 24,666 signatures he needed, the only hope is a write-in campaign, something the Constitutionals are preparing.

Mr. Winger, though, warns that he's in for a disappointment.

Laws notwithstanding, he said, roughly one fourth of the state's counties don't even bother to count the write-in votes.

"Counties like Philadelphia, and certain others, just ignore them," he said.