KITTY PILGRIM: The development of the missile defense shield is a big priority for President Bush, so U.S.-Canada relations hit a rough patch with this statement from Canadian Prime Minister Paul Martin.

"We are announcing today that Canada will not take part in the proposed ballistic missile system. "

Canadian public opinion opposed the war in Iraq, and now most oppose participation in the U.S. missile shield. So many experts say Paul Martin made the statements for political reasons.

JACK SPENCER, HERITAGE FOUNDATION: At the end of the day, if a ballistic missile comes headed towards Canada, whether they participate or not, the United States will, in all likelihood, intercept that ballistic missile.