PROVIDENCE — The Moderate Party may be reaching its end in Rhode Island, where its founder ended his five-year venture this week and said he’d be making his second run for governor as a Republican.“The results speak for themselves,” said Ken Block, who poured hundreds of thousands of dollars into his own and other candidacies. Not a single candidate has won elected office as a Moderate.Past supporters of the Moderates said they believe the party is finished, and so it is likely to meet the fate political experts say often befalls third parties: extinction, failure or irrelevance.“There’s so many institutional barriers in favor of the two major parties that it’s virtually impossible to launch a successful third party,” said Darrell West of the Brookings Institution public policy think tank in Washington. He cited a lack of media coverage, fundraising difficulties and trouble getting on the ballot as the chief problems that face third parties in the U.S., such as Libertarians, Greens and the Reform Party.Block launched the Moderates in 2008 as an alternative to Republicans and Democrats, saying those parties were too focused on polarizing social issues and not enough on fixing Rhode Island’s problems. He fought and won an early legal battle to make it easier for new parties to collect signatures to put candidates on the ballot.The party attracted support from some high-profile people within the state, including former Hasbro CEO Alan Hassenfeld, former Republican Attorney General Arlene Violet and former U.S. Attorney Robert Clark Corrente, who served for a time as the party chairman.More recently, Block, as head of the Moderate Party, has pushed an end to straight-ticket voting, in which voters may cast a ballot for all candidates of a certain political party with a single vote. That position was later adopted by officials including Democratic Secretary of State Ralph Mollis.Wendy Schiller, a political science professor at Brown University, said that’s often how it goes with third parties.“Third parties in general in American politics are most successful in getting a particular issue on the agenda, and once that issue is on the agenda, typically they fold,” she said.She said it goes back as far as the Free Soilers of the mid-1800s, a party that opposed slavery but was short-lived even as its ideas were adopted by the Republican Party.Block was his party’s first candidate for governor in 2010, when he received just 6.5 percent and came in fourth behind the Republican, the Democrat and then-independent Lincoln Chafee, who won. Chafee is now a Democrat and not seeking a second term.Block said he now realizes he can’t change anything by continuing on with a third party, an idea he said is not feasible in Rhode Island or anywhere else.“This is about understanding at some point when an approach doesn’t work, and that approach doesn’t work,” Block said. “A tremendous number of individuals even today are like, ‘What is the Moderate Party? I don’t get it.’ ”Block is taking a well-traveled road by joining the Republicans and trying to change it from within, West said. That’s what’s happened with tea party activists in recent years.As of this month, about 1,500 Rhode Island voters were registered Moderates, compared with 74,000 Republicans, 290,000 Democrats and more than 360,000 unaffiliated with any party.The future of the party Block founded isn’t clear. He closed the party’s bank account, which was almost empty. The Moderate Party earned an automatic place on the ballot this year because Block received more than 5 percent of the vote in the 2010 gubernatorial race.But Hassenfeld, for one, said he doesn’t know who would step in.Joe Botelho, who lost last year as a Moderate for a state House seat, said Block ran the party in an insular way, and he didn’t know of anyone else who would take over. He said he has already changed his party affiliation back to what it had been for most of his life, until the Moderate Party came along: Democrat.