If Australian opposition leader Bill Shorten becomes prime minister and visits the U.S., he can expect questions about a radio interview he gave three years ago in which he said some of then-presumptive Republican presidential candidate Donald Trump's views were "barking mad."

Trump seemed a long shot for the White House when Shorten gave the interview on May 27, 2016, during Australia's last election campaign.

And Shorten, who leads the center-left Labor Party, seemed a long shot to become Australia's prime minister.

He was trying to become the first Australian opposition leader to oust a prime minister after a single three-year term since 1931, when the Great Depression helped scuttle a Labor government.

But Shorten came closer than many had expected.

Conservative Prime Minister Malcom Turnbull scraped back into power with a single-seat majority in the House of Representatives, where parties need a majority of seats to form a government. Turnbull's conservative coalition had lost 14 lawmakers.

Turnbull pounced on Shorten's swipe at Trump as evidence that the Labor leader wasn't fit to lead Australia.

Turnbull accused Shorten of potentially offending Australia's most important strategic ally by breaking a long-standing Australian convention of avoiding taking sides in U.S. political contests.

Shorten had told a Darwin radio station that a Trump administration was among "the sort of scenarios you hope don't emerge."

"I think Donald Trump's views are just barking mad on some issues," Shorten said.

"America's a great friend of Australia; whoever they dish up we'll work with, but wow, Trump's sort of — it's sort of the ultimate victory of celebrity politics," he said.

Shorten described Trump's popularity as the "ultimate protest vote," and warned that Australia should pursue policies of fairness and equality.

The political landscapes in Australia and the United States have transformed since 2016.

Shorten's party goes into the 2019 election campaign as a firm favorite. His party has led the conservative coalition in most opinion polls in the last three years.

Turnbull was replaced by senior minister Scott Morrison in a revolt by ruling Liberal Party lawmakers at least partly because of the government's poor performance in opinion polls.

The government lost two lawmakers and its majority in continuing blood-letting from the leadership change.

Despite Labor's dominance in the polls, Shorten's personal popularity has remained relatively low. But Australia's system of compulsory voting means Shorten's lack of charisma is not the political handicap it might be in U.S politics.

Because failing to vote is punished with a fine, voter turnout in Australia is always high even when the choices are not particularly attractive.

While there are Labor lawmakers who are more popular with the Australian public, Shorten is a power broker who has enjoyed strong support within his party for the past six years of his leadership.

The government had depicted Shorten as a puppet of the labor unions that donate to Labor's campaign war chest.

The government has also portrayed Shorten as being reckless with policies that would harm the Australian economy.

Energy policy is as contentious as any in Australia, which is the world's biggest exporter of coal and liquid natural gas.

Labor wants to cut Australia's greenhouse gas emissions by 45 percent below 2005 levels by 2030.

Australia committed in the Paris Agreement on climate change to reduce its emissions by 26 or 28 percent by 2030.

Shorten, 51, was first elected to Parliament in the same 2007 election that swept Labor to power for the first time in more than 11 years. Morrison entered Parliament in the same election.

Shorten has deep labor union roots. His father was a waterside laborer and union official, and his mother was a lawyer and university academic. He became involved in Labor politics as a student and was soon touted as a potential prime minister. He worked for less than two years as a lawyer before becoming a union official.

Shorten first came to national attention as national secretary of the Australian Workers Union in 2006 when the Beaconsfield gold mine collapse in Tasmania state killed one miner and left two trapped underground for two weeks.

His regular news conferences on behalf of the union representing the miners created a national profile before he entered Parliament the following year.

But as a party power broker, Shorten played a key role in deposing two prime ministers through internal government leadership ballots in the face of poor opinion polling during Labor's chaotic six years in office. His history of fickle loyalty in ousting leaders he once supported may come back to haunt him as he seeks to lead the country.