Syrian President Bashar Assad sounded a defiant note Wednesday on the eve of a Mideast visit by US President George W. Bush, amid reports that some in Washington want Syria's help in calming Iraq. "Challenge is the most precious thing we possess, so we will keep challenging until we achieve our goals," Syrian official media quoted Assad as saying Wednesday. The day before, his message was even sharper, although he did not refer directly to Bush. "We send a message to every one that Arabs are no longer a herd that can be sold, bought and taken to the slaughterhouse," he said Tuesday in the speech in the southern city of Sweida. Bush was arriving late Wednesday in Jordan for a summit with Iraqi Prime Minister Nouri al-Maliki in a fresh attempt to put an end to violence in Iraq.