OTTAWA -- The prime minister is jetting out of Ottawa today, leaving behind one of the worst political storms ever faced by his Conservative government, to contemplate a trade alliance membership in South America that many consider unnecessary.

Before he leaves, though, Stephen Harper is expected to address the Conservative caucus and talk about his right-hand man, Nigel Wright, who resigned Sunday as a result of his role in a ballooning controversy involving the disallowed expenses of Sen. Mike Duffy.

Wright wrote Duffy a personal cheque for $90,000 to cover the senator's improper housing claims, a quiet transaction critics say violates ethics rules prohibiting senators from accepting gifts.

The embattled Duffy quit the Conservative caucus last Thursday. Sen. Pamela Wallin, who is facing her own expenses audit, "recused" herself from caucus on Friday.

The expenses controversy is fast becoming one of the most serious challenges faced by Harper's administration — MP's have been hearing from upset constituents, the ethics commissioner is investigating the matter and the NDP yesterday asked the RCMP to probe Wright's actions as well.

The New Democrats have also called on Harper to publicly explain the entire matter to Canadians and make clear exactly what he knew and how he feels about what happened.

The whole imbroglio makes for an ugly backdrop for Harper's trip to Peru, where he'll engage in bilateral talks with that country's leader before travelling to Columbia for meetings with the Pacific Alliance trade group.

The alliance was formed in 2011 by Chile, Colombia, Mexico and Peru; Canada took a spot as an observer the following year, along with several other countries.

A spokesman for Harper said the alliance talks will be the first time the prime minister can fully experience what the forum has to offer.

The alliance aims to do away with what economic borders remain between their countries, creating an integrated market.

But Canada already has free trade agreements with all four alliance countries and is involved in negotiations for the much broader Trans-Pacific Partnership, which includes them as well as Asian countries, New Zealand and the United States.

That's raised questions, even from pro-trade Conservatives, about why joining the new alliance is something that Canada needs — and whether it has the resources to tackle the task.

For more from the Canadian Press, click here or scroll down The Tyee's main page.