It’s dangerous because Australia fully renounced its discriminatory White Australia immigration policy only in 1973. Since then, nondiscrimination has been a cornerstone of Australia’s social evolution, something both major parties have proudly regarded as nonnegotiable.

When John Howard as opposition leader suggested in 1988 that Australia should consider merely slowing the rate of Asian immigration, he lost his job and, many thought, his political career. It took him until 1995 to reattain his leadership role. Yet today, Mr. Howard’s remarks seem mild.

But it’s also dangerous because of the moment we’re in. Mr. Trump’s gravitational pull is visible in the resurgence of the far-right, nationalist One Nation Party, which wants not only to ban Muslim immigration, but also to convene a commission to determine if Islam is a religion or political movement.

Naturally, Pauline Hanson, the One Nation Party leader, tweeted that Mr. Trump’s policy was “a good start, but I would go further.” The Turnbull government has members of its own backbench who share similar sentiments. One explicitly declared, “I think Trump has got it right.” Another — who met with Rudolph Giuliani and Kellyanne Conway during the campaign and wants to “make Australia great again” — has established his own breakaway party. And while it is true these views are on the fringes of our Parliament, they are not entirely relegated to the margins of public opinion.

Australia is now a nation where, according to an opinion poll from last year, 49 percent support a ban on Muslim immigration, a result so shocking the pollsters did it twice before releasing it. A similar poll the previous year had that figure at 28 percent. Even allowing for the vagaries of polling data, those results signal a remarkable change in a short period. In the aftermath of Mr. Trump’s ban, another poll found 44 percent of Australians supporting similar measures.

Australia’s asylum-seeker policies were meant to prevent all this. The pious calculation is that by making a show of our iron borders, Australian multiculturalism can be protected. Shunting asylum seekers offshore bolsters public confidence in our migration system, which preserves our tolerance of the migrants who are here. Yet for all that, it now seems Australian attitudes are getting harsher.

Perhaps it’s true that, absent our current policies, those attitudes would be worse still. But it may also be true that when you spend 15 or so years deriding asylum seekers as “illegals” or “queue jumpers,” describing their arrival as a “peaceful invasion” or warning they might be terrorists, it all lodges in the public imagination. Perhaps, far from leading to a more thorough acceptance of migration, this constant demonization of migrants establishes a norm of selective xenophobia where exempting a group of migrants from our tolerance is unremarkable.

I understand the difficulty of Mr. Turnbull’s position. But the reaction here to Mr. Trump represents the resurgence of our worst instincts. We’re doomed if, in the face of this flirtation, the best we can muster is silence.