Prime Minister Justin Trudeau acknowledged Thursday that the Liberals didn’t run in 2015 on a plan to buy a pipeline, but he defended the purchase as an economic necessity.

Trudeau attended a town hall event at the University of Regina – his second town hall event this week -- where audience members were invited to ask questions of the prime minister.

One of the toughest questions came from a man wearing an “I love pipelines” T-shirt, who admitted he didn’t like Trudeau and asked him to explain why his government spent $4.5 billion to save Kinder Morgan’s contentious pipeline expansion.

Trudeau said Ottawa stepped in because Kinder Morgan “wanted to throw up their hands and walk away,” and his government wanted to make sure that Canadian oil could reach new markets.

“It is not, as you pointed out, in my platform that I was going to buy a pipeline for Canadians, but it was in my platform that I was going to grow the economy and protect the environment at the same time and do it in thoughtful and responsible ways,” Trudeau said.

The prime minister said it is “it is an absolute priority” to diversify Canada’s oil exports to countries besides the United States, and said Canadian workers -- particularly in Alberta and Saskatchewan -- are “prisoners” due to the current situation.

“Ninety-nine per cent of our oil goes to the United States right now. On top of that, the United States is sometimes a challenging partner to deal with. It makes sense to diversify to markets in Asia,” Trudeau said.

“The Trans Mountain Pipeline expansion will allow meaningful impacts on that, and that is why we made the decision that the federal government should take over the pipeline expansion project.”

Trudeau also addressed the decision to sign the U.S.-Mexico-Canada trade deal, USMCA, despite continued steel and aluminum tariffs from the U.S.

The decision, Trudeau said, boiled down to two choices.

“Do we sign the new NAFTA with our largest and most important trading partner and pledge to continue to look for moments to pressure the U.S. to remove these steel and aluminum tariffs, or do we walk away from a $2-billion-a-day trading relationship that is hugely important for the Canadian economy?” he said.

“Securing NAFTA at a time of unpredictability and protectionism in the United States was a massive priority for all Canadians and we did it and we did it together.”

While the tariffs are still in place, Trudeau said his government is still working with U.S. lawmakers on the legislation, which hasn’t been ratified by Congress.

“And every single conversation I’ve had with the president, I bring up the fact that these tariffs are not just hurting Canadian workers like yourself and Canadian companies, they’re also hurting American workers and American companies and we’re seeing increasing stories on that.”

The Regina event was the second time this week Trudeau has taken questions from the public in a town hall. Earlier this week, he addressed similar questions about pipelines in Kamloops, B.C.