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The horrors of chemical warfare in Syria, and the vacillation by Western leaders in response, offer important lessons in how and when parliaments may check the authority of a president or prime minister to wage war in all but name.
Barack Obama in Washington; David Cameron in London; François Hollande in Paris; Stephen Harper in Ottawa. All have discovered the extent to which they are constrained, by constitutional convention or political reality, from projecting force without seeking the assent of the people's representatives. Of the four, only Mr. Harper appears to have emerged from the experience unscathed.
Mr. Obama surprised his own aides when he announced over the Labour Day weekend that he would seek congressional support for military action against the Assad regime over its alleged use of chemical weapons.
By convention, Mr. Obama could have ordered the attack on his own authority. But even though the action would consist only of missile strikes, a war-weary public appears to want none of it. Mr. Obama's decision to consult Congress is most likely an attempt to provide himself some political cover for the attack (and possibly to expose internal divisions within the Republican Party in Congress).
Nonetheless, the distinguished Canadian political scientist Richard Simeon applauded the decision.
"When you're in a dicey area like this, it's always best to consult the people or consult the parliament," he said in an interview. "We already concentrate far too much power in the executive, and the power to make war is a pretty horrendous power."
The U.S. Constitution states that only Congress may declare that a state of war exists between the United States and another country. But that hasn't happened since 1941, when the United States went to war against the Axis powers.
Congress has, however, approved resolutions authorizing the use of force, such as the 2003 war in Iraq, or approved an action authorized by the United Nations Security Council, such as the Korean War in 1950 or the Gulf War in 1990.
And sometimes, as in 1983, when president Ronald Reagan ordered the invasion of Grenada, a president has acted on his own authority.
One check on that authority is whether the action is large enough, or lasts long enough, to require congressional authorization for funding.
"While the executive may have the authority to involve the United States in some kinds of conflict, the fact is that Congress, and in particular the House of Representatives, has control of the purse," observes the constitutional scholar David Smith of Ryerson University.
Britain and Canada are governed by the largely unwritten Westminster constitutional system, which vests the authority to wage war in the Crown – effectively the prime minister. But after the debacle in Iraq, British Prime Minister David Cameron felt compelled to seek the approval of Parliament before joining the United States in attacking Syria, only to be rudely rebuffed by the House of Commons.
The French constitution gives François Hollande the authority to attack Syria without seeking the approval of the National Assembly, but the French President acknowledged on the weekend that France will not – actually, cannot – launch an attack unless the Americans take the lead.
In Canada, prime ministers sometimes do and sometimes don't consult Parliament before deploying military force. In 2006, Stephen Harper sought the consent of the House before committing Canadian forces in Afghanistan, and did the same before the Libyan mission.
"It is fair to say there is a precedent for, and growing expectation of, parliamentary debate and consultation before Canadian participation in significant international military campaigns," said Lorne Sossin, dean of law at York University's Osgoode Hall Law School, though he added that the precedents are too recent and too few to constitute a proper constitutional convention.
But Mr. Harper did not seek parliamentary approval before offering logistical support to French forces in Mali. Nor did he feel the need to consult Parliament before offering only diplomatic support for an attack on Syria. So the precedent appears to be limited to actions that involve actual combat.
Add it all up and you get an American president forced to go to Congress for political cover before he strikes Syria; a British prime minister who sought parliamentary approval to join that strike, but was turned down; a French president who does not need or plan to seek parliamentary approval for a strike, but who lacks the military strength to launch one unless the Americans go in first, and a Canadian prime minister who is, no doubt, quite happy that he decided to sit this one out.
It makes for a fascinating political seminar on the evolving limits of executive authority – or it would, were the events that prompted these debates not so grim.
John Ibbitson is the chief political writer in the Ottawa bureau.