Opposition leader Bill Shorten has criticized U.S. Republican presidential candidate Donald Trump, saying that the presumptive nominee will be “difficult to deal with”.

The Labor leader made these comments during a campaign visit to South Australia, where he revealed his own take on the primary contenders to succeed Barack Obama, who will step down from office this year.

“I have to say that if I was in America, I’d be voting for Hillary Clinton,” Shorten said, according to ABC News. “Whoever America elects we’ll deal with, but there’s no doubt in my mind that Trump would be difficult, I think, to deal with.”

When asked about the kind of difficulties he’s referring to, Shorten abruptly replied: “Have you read what he [Trump] has said?”

Despite his opposition towards a Trump presidency, Shorten guaranteed that Australia will work with whoever is elected. “Ultimately, the American presidency will be decided by American voters,” he said.

Foreign Affairs Minister Julie Bishop remarked on Shorten’s comments, saying that he must be specific and explain the areas of difficulty that would arise from a Trump presidency.

Additionally, Bishop also said that Shorten should explain whether the Australia-US alliance would be scrapped or downgraded by a Labor-Greens government, according to the Sydney Morning Herald.

Shorten isn’t the only Australian politician to slam Trump and express doubts about his capabilities of becoming president.

Australian politicians have brought up Trump’s name and his candidacy during the campaign period in light of comments made by Greens leader Richard Di Natale.

Di Natale has urged Australia to cut ties with the U.S., and has been condemning the decision to join the U.S. in the country’s military actions over the last century.

Shorten slammed Di Natale for his comments, especially for suggesting that Australia would be joining a “regional arms race”, saying that the Greens had “silly positions on a range of matters.”