Outgoing Canadian Ambassador to the U.S. Gary Doer says security is going to be the biggest challenge for Canada and the United States in the years to come.

In a sit-down interview with CTV鈥檚 Power Play, Doer said the allies will have to continue to work together in the fight against terrorism at home and abroad.

鈥淲hat is going to be the most challenging issue facing Canada and the United States in the next period of time, it鈥檚 going to be keeping the world safe and keeping our neighbourhoods safe.鈥

Doer recounted U.S. President Barack Obama鈥檚 immediate support following the Oct. 22, 2014 terror attacks in Ottawa. 鈥淲e had 鈥 President Obama stand up and 鈥 offer his condolences to the Canadian people, to the Canadian military, and again speak to the relationship that we have not only as friends but as partners in keeping our neighbourhoods safe. And that鈥檚 crucial going forward.鈥

Doer, whose six-year stint in Washington wraps up next year, warned that there will always be ups and downs between Canada and the U.S. For instance, while the U.S. rejection of the Keystone XL pipeline was a setback for Prime Minister Justin Trudeau and Obama, Doer said the climate change talks in Paris marked a positive meeting for the two leaders.

鈥淚 expect Canada-U.S. relations to continue to move forward, but I also know that with $2 billion of trade a day, and sharing all the water and lakes we have, and the ecosystem we have, we will always have a bit of speedbump in our relationship,鈥 said Doer.

鈥淚 don鈥檛 want to sugar coat anything. There鈥檚 going to be disagreements. We鈥檙e two sovereign countries.鈥

Those words of advice will be important for the next ambassador 鈥 an appointment Trudeau will have to make early in his mandate.

Devil鈥檚 Brigade recognition highlight of ambassadorial career

The envoy job comes with many perks and thrilling moments. But for Doer, his visits to the Oval Office and the Pentagon weren鈥檛 the highlights of his time in Washington. Rather, it was the awarding of the Congressional Gold Medal to the Devil鈥檚 Brigade, an elite Second World War commando unit.

鈥淚t took us four years to finally get approval of the Congressional Gold Medal,鈥 said Doer. 鈥淎nd making the point that these people were 88, 89, 90 years old.鈥

The unit, comprised of Canadian and U.S. soldiers, were the precursors to today鈥檚 Special Forces, including Canada鈥檚 Special Operations Regiment and the U.S. Navy Seals. The men took on some of the most dangerous and difficult missions in the war, never losing a single one of the 22 battles they fought. .

U.S. election will be 鈥渇ought in the middle鈥

Doer acknowledged Donald Trump鈥檚 lead in the Republican presidential pack, but said it鈥檚 too early to predict the 2016 election outcome. He said that candidates appeal to the 鈥渆xtremes鈥 in their parties during the primaries stage of the election, but that the vote is fought and won in the 鈥渕iddle.鈥

鈥淭he American public in places like Florida, Pennsylvania, Ohio, Colorado, New Mexico, Virginia, North Carolina, they鈥檙e kind of middle voters and they will determine, under the electoral voting system, who the president is. And they always get it right.鈥