Justin Trudeau broke a campaign promise on Tuesday. And it might be the smartest decision his fledgling government makes in the next four years.

By acknowledging his government won't meet its deadline of resettling 25,000 Syrian refugees in Canada before the end of the year, the prime minister acknowledged that the ISIS-sponsored attacks in Paris this month have heightened Canadians' concerns about security.

"This is about welcoming people who are fleeing terrorism, not bringing terrorism with them," Trudeau said in an interview with CBC Radio's Matt Galloway on Tuesday.

Assuaging fears. Listening to Canadians. Those are the points cabinet ministers took pains to highlight Tuesday when announcing details of the revised plan.

"I have heard Canadians across this country saying, 'Yes, you have to do it right, and if takes a little longer to do it right, then take the extra time,'" Immigration Minister John McCallum said in announcing the details of the revised plan.

Immigration Minister John McCallum says the Liberals didn't break their campaign promise to bring in 25,000 Syrian refugees, but Conservative Immigration Critic Michelle Rempel disagrees. 1:23

What wasn't said was equally important. The sheer numbers to be resettled, despite the good will and the significant government resources the Liberals were committing to the process, made their own self-imposed deadline all but impossible to meet.

"It's the right thing to do,'' said Carleton University professor James Milner, a former consultant with the UN High Commissioner for Refugees. "Every expert I know has been saying get the process right."

Getting it right means more than getting 25,000 people into Canada by an arbitrary deadline set out in an election campaign. The photo of the lifeless little body of three-year-old Alan Kurdi face down on a Turkish beach thrust the humanitarian crisis in Syria into prominence during the campaign, especially after it was reported the Kurdi family had hoped to come to Canada.

The Conservatives moved up their pledge to bring in an additional 10,000 refugees by 15 months, to September 2016. The NDP promised to resettle the same number by the end of the year. The Liberals went the furthest with their ambitious — and what their opponents called unrealistic — target.

Conservative immigration critic Michelle Rempel said the Liberals' campaign promise was made without any plan or realistic assessment of the cost to taxpayers and to provincial governments, which are responsible for housing, education, health and social services.

Immigration, Refugees and Citizenship Minister John McCallum says the additional time will allow for better preparations for the thousands of Syrian refugees coming to Canada. (Fred Chartrand/Canadian Press)

There's also some concern that the 25,000 refugees won't all be sponsored directly by the government, but include those already being sponsored by churches and other private groups.

But Milner said the delay shouldn't be viewed as a broken promise.

"This is a government that promised transparency and evidence-based decision-making," he said. "If the extension of six to eight weeks gives Canadians more confidence in the process, that's a good thing."

Details of revised plan

Under the revised plan, Canada will identify the 25,000 refugees it plans to resettle by Dec. 31, with 10,000 of those now slated to arrive in Canada by the end of the year. The rest will arrive by the end of February 2016.

Trudeau told CBC that pushing back the deadline will ensure the resettlement process is done right and will create a better chance for their successful integration into Canada.

"We want these families arriving to be welcomed, not feared, because that's the way to get the right start in terms of having them become valuable parts of our community and create success."

The government also said the eight-week extension allows security and health screening to be completed overseas, not in Canada, addressing concerns raised by Saskatchewan Premier Brad Wall and a number of big-city mayors across the country, among others.

"My counsel would still be to the prime minister that we ought to just suspend the deadline,'' Wall told reporters this week in Ottawa.

Aftermath of Paris attacks

The attacks in Paris that killed 130 people and seriously wounded many others stunned people around the globe. Fears grew that ISIS extremists have infiltrated the mass human migration out of Syria.

In the United States, pressure to suspend refugee-processing grew. About two dozen governors are insisting they won't allow Syrian refugees to resettle in their states.

But national leaders — including U.S. President Barack Obama —attending the G20 and APEC summits last week insisted that what happened in Paris should not be linked to assisting refugees.

Still, Trudeau said the attacks underscored the importance of doing the health and security screening of refugees overseas, to ensure the ''few people who will be surprisingly problematic'' won't already be in Canada, where the charter and other legal avenues make it difficult to remove anyone deemed inadmissible.

A man kisses his child on a beach after crossing the Aegean Sea in a dinghy with other refugees and migrants from Turkey to the northeastern Greek island of Lesbos. (Santi Palacios/Associated Press)

Trudeau also responded to a CBC story this week that said the government's plan will give priority to families with children.

He argued they are the most vulnerable, but dodged questions about why single men — including the father of Alan Kurdi, who lost both his sons and wife while trying to escape Syria — are given less priority.

"Families are certainly easier to place and easier to draw in on an accelerated basis than some other categories."

Milner said that's consistent with the UN's own mandate, which gives priority for resettlement to several vulnerable categories, including women and children. He said they make up 80 per cent of refugees.

"My read is that the majority who will come in the initial steps are families, and that makes sense."

So the pressure is eased, for now. And the Liberals have shown they're not only prepared to listen, but to respond to what they hear.