From the WSJ article:
we'd point to some clear, public evidence of an Iraq-al Qaeda link that the media have overlooked in their fondness for cloak-and-dagger sourcing.
Mr. Bush has been blunt on the point, for starters. In his October 7 Cincinnati speech, he noted that Iraq and al Qaeda have "high-level contacts that go back a decade" and that a "very senior" al Qaeda leader was in Baghdad this year for medical treatment. Also, "Iraq has trained al Qaeda members in bomb-making and poisons and deadly gasses."
As for "intelligence sources," America's most prominent is CIA Director George Tenet. A recent letter in his name to Congress laid out the following evidence, which we reprint at length since everyone else seems to have ignored it:
"*Our understanding of the relationship between Iraq and al-Qaeda is evolving and is based on sources of varying reliability. Some of the information we have received comes from detainees, including those of high rank."*We have solid reporting of senior level contacts between Iraq and al-Qaeda going back a decade.
"*Credible information indicates that Iraq and al-Qaeda have discussed safe haven and reciprocal nonaggression.
"*Since Operation Enduring Freedom, we have solid evidence of the presence in Iraq of al-Qaeda members, including some that have been in Baghdad.
"*We have credible reporting that al-Qaeda's leaders sought contacts in Iraq who could help them acquire W.M.D. [weapons of mass destruction] capabilities. The reporting also stated that Iraq has provided training to al-Qaeda members in the areas of poisons and gases and making conventional bombs.
"*Iraq's increasing support to extremist Palestinians coupled with growing indications of a relationship with al Qaeda, suggest that Baghdad's links to terrorists will increase, even absent U.S. military action."
Presumably Mr. Tenet wasn't making all of this up, and presumably his claims are based on the work of his own "sources" in the U.S. intelligence community.
If you're waiting for the sort of proof that would hold up in court, that probably won't be available until after Iraqi regime change, if then. But the evidence cited in the WSJ article is proof enough for me.