There's been a lot of third-party talk among Republicans lately. Weekly Standard editor Bill Kristol is perhaps the most prominent conservative leader to say we need "a new party" if Donald Trump wins the GOP nomination. Trump, who flirted with seeking the 2000 Reform Party nomination, has occasionally threatened to desert the Republicans if they don't pick him as their presidential candidate.

All this runs counter to the lessons of the country's recent election cycles. Trump has been so successful in part because, unlike Ross Perot, he doesn't have to divert his considerable resources into making an independent candidacy viable. He's running as a third-party candidate within the Republican Party itself.

This guarantees him huge exposure during the primary campaign. It prevents him from wasting time and effort just to get on the state ballots, where the game is rigged in favor of the two-party system.

Is Trump anomalous because he is so controversial and famous? Not necessarily. There's no special magic to the Republican or Democratic parties, but the American political system has existed so long divided along these lines that the whole system works to support major party candidates, pretty much exclusively. And even someone as rich as Trump can't change that.

Longtime political independent Bernie Sanders has also realized the benefits of sticking with a major party, even one he doesn't particularly like. Sanders was affiliated with a bevy of obscure Vermont third parties and was elected to both the House and the Senate as an independent, sometimes running against the official Democratic nominee. But even running against a formidable politician like Hillary Clinton, Sanders has done a much better job of getting his message out running as a Democrat than he would if he were trying to go it alone.

Sanders appears on stage with Clinton (albeit at a relatively small number of debates scheduled on busy Saturday nights of Christmas shopping, Star Wars, and football), has been a guest on most of the major talk shows, and is receiving serious media coverage.

The Vermont socialist also has the opportunity to present his policy agenda for millions to endorse in the Democratic primaries even if he never gets close to the nomination. This includes thousands, and perhaps millions, of Democrats who would be reluctant to cast even a protest vote for a third-party candidate on the left after the Ralph Nader experience of 2000, where progressives picking the longtime consumer advocate diverted votes away from the Democrats, and probably cost Al Gore the election.

Sanders, just like Trump, is running as a third-party candidate within a major party. This isn't the first time Sanders has recognized the benefits of working within established Democratic power channels in his career. Sanders has been more effective in Congress because he has caucused with the Democrats and his Senate seat has become more secure since national Democrats recognized him as (basically) one of them rather than someone to replace with a real Democrat.

The examples go back much further than that. Ron Paul had a bigger impact on the national debate finishing a distant fourth in the Republican primaries in 2008 and 2012 than he did winning the Libertarian Party nomination in 1988.

Gary Johnson, the 2012 Libertarian nominee, was a success story because he won more than 1 million votes in that election. But Ron Paul won more than twice that in the GOP primaries alone that year. And as a Republican, Johnson served two terms as governor of New Mexico. He was not just a rounding error in a contest between Barack Obama and Mitt Romney.

Didn't Howard Dean do more to move the Democratic Party to the left than Nader, who helped cost the Democrats the election in 2000? Didn't Pat Robertson's 1988 presidential campaign do more to mobilize conservative Christian voters than the Constitution Party has done in more than a quarter century since then?

Many conservatives have long been grateful that Ronald Reagan spurned advice from the likes of longtime National Review publisher William Rusher and stuck with the GOP rather than going out and creating a third party. Third parties are great for protest votes, which can be important. But when it comes to influencing policy, major parties are where the action is.