As Howard Schultz ponders a U.S. presidential run, here's a look at other independent upstarts

Howard Schultz, who helped turn Starbucks from a little-knownregional coffee chain into an international food service powerhouse, said on Sunday he was pondering a U.S. presidential bid as a "centrist independent."

Schultz's name had been bandied about as a possible 2020 contender, though some assumed he would vie for the Democratic Party's nomination. This past weekend, he posted a series of tweetstimed tocoincide with a 60 Minutes appearance on Sunday, as well as a book tour this week.

The former Starbucks CEO has evidently decided he didn't have enough supportwithin the Democratic Party. Prominent Democrats were quick to discourage him from an independent bid, believing without any evidence that he could siphon votes from the Democratic candidate in what they see as a winnable election (against, presumably, Donald Trump).

There have been significant barriers to candidates who don't secure the Republican or Democratic nomination, as the primary process caters to registered party voters. As well, each party has its own established fundraising operations.

Here's a look at the most notable third-party or independent candidates in modern U.S. history.

George Wallace, 1968

American Independent Party

Election showing: 9.9 million votes, 13.5 per cent of the total, fivestates carried

Wallace, a Democrat in his home state of Alabama, was out of step with the national partyowing to his segregationist views, just three years afterPresident Lyndon Johnson unveiled asuite of domestic programs to improve the rights of minorities. Wallace's differences with the party were so pronounced that at the 1968 Democratic convention, fellow Alabama legend and Crimson Tide football coach Bear Bryant received more delegate votes for presidentthan Wallace and Bryant wasn't even running.

But by that time, Wallace had obtained enough signatures to put himself on the election ballot while leading the American Independent Party. It was a tumultuous year: President Johnson announced he wasn't seeking re-electionand Democratic SenatorBobby Kennedy wasassassinated. The Democrats' candidateended up being Hubert Humphrey, then the vice-president.

Wallace managed to pickup Alabama and four other southern states in the November election.But even in the unlikely event that all of those electoral votes would have gone to Humphrey, Republican Richard Nixon would still have prevailed by a comfortable margin.

In 1972, Wallace was a significant factor operating within the Democratic primary process, winning six states. But then he, too, was felled by an assassin. It ended his campaign in May and left him paralyzed for life.

John Anderson, 1980

National Unity Party

Election showing: 5.7 million votes, 6.6 per cent of the total

Anderson had a nearly two-decade record as a Republican congressman, but found himself at odds with what he called the hawkish direction of the party. He supported gun control measures and a co-sponsored a gay rights bill in the House. A bid for his party's nomination was not in the cards with heavy hitters like Ronald Reagan and George H.W. Bush in the running.

The bespectacled, professorialAnderson set out on his independent bid as leader of the American Unity Party. He was seen as so liberal within his own party that some Republican operatives cheeredhimon, believing he would be more likely to receive support from Democratic voters disillusioned with Jimmy Carter's first term.

Anderson received 5.7 million votes, still the fourth-highest ever showing among non Republican, non-Democrat candidates.

Ross Perot, 1992 and1996

Election showing in 1992: 19.7 million votes, 19 per cent of the total
1996: Eight millionvotes, eight per cent of the total

Perot becamea billionaire by developing growing and selling Electronic Data Systems, and in 1992, theTexan opted to fund his own presidential campaign.

Perotpreferred to relayhis plain-spoken message in television interviews and infomercials, rather thanpressing the flesh at diners and swap meets.He gained purchase by attacking George H.W. Bush's taxation and economic policies, including NAFTA, and became a cultural phenomenon in his own right,inspiring Saturday Night Live and other late-night skits owing to hiselfin appearance and high-pitched twang.

Perot also revealed his flightiness he dropped out of the race in July, citing the revitalized strength of the Democratic Party,before re-entering three months later.

Even so, Perot had more success than any third-party candidate in 80 years, and it has become an accepted narrative in some quarters that Perot cost Bush the 1992 election.One poll estimated that about 70 per cent of Perot voters had gone for Bush over Michael Dukakisin 1988. But in general, Perot did best instates that Bush carried in the winner-take-all electoral college system.

Perot tried again in 1996, under the imprimatur of the Reform Party, taking eight per cent of the vote (eight million overall) but carrying no states.

Ralph Nader, 2000

Green Party

Election showing: 2.8 million votes, 2.7 per cent of thetotal

There was something in the air in 2000. Donald Trump, with adviser Roger Stone often at his side, teased a potential bid as a Reform Party candidate. He didn't end up going through with it, and that party ended up fieldingright-wing firebrand Pat Buchanan, who had made some waves in the 1992 and 1996 Republican primaries.

Consumer advocate Nader was an easy convert to the notion of smashing the two-party system, having once backed Dr. Benjamin Spock of the People's Party in the 1972 campaign.

"They never tell us when we're permitted to engage in a protest candidacy," Nader said in a 2016 interview with CBC News. "When is the right time? It never is."

Democrats still fume aboutNader's supposed negative impact on Al Gore's bid against Republican George W. Bush. Bush's victory all came down to aremarkable fight in Florida involving ambiguous ballots and a Supreme Court decision.

Naderinsisted the outcome had nothing to do with his voters. As Nader told CBC News, "a big bloc of my votes were voters who would have stayed home otherwise."

It's a contention backed up by at least one study of Nader and Gore voters from 2000.

Gary Johnson & Jill Stein, 2016

Johnson (Libertarian Party): 4.4 million votes, 3.3 per cent of the total
Stein (Green Party): 1.4 million votes, one per cent of the total

Outgoing president Barack Obama said any third-party vote in the 2016 election would be "a vote for [Donald] Trump." Bernie Sanders also urged his supporters to back Hillary Clinton, who had defeated him in a bitterDemocratic primary. After all was said and done, Trump's razor-thin wins in a handful of battleground states gave Clinton supporters ammunition to suggest her bid to become the first female president was scuttled in part by independents, especially Green Party candidateJill Stein.

Both Johnson and Stein had had a run for president in 2012, but they seemed to get more media attention four years later, in a race without an incumbent, and two divisive contenders. Johnson's campaign included a notable gaffe in which he seemed to lack knowledge regarding Syria's war, but it's unclear if it moved the needle substantially on his ultimate performance.

WithJohnson and Stein part of the equation, Trump won the presidency with just over 45 per cent of the popular vote vote,the lowest percentage for a winner since Bill Clinton in 1992.