I don't know or much care who your sources in the OP are talking about but people raising a few pot plants in their basements clearly don't finance terrorism but they get busted and sent to jail, sometimes for a very long time. Ironically the world's largest drug producers and smugglers worked with impunity under the benevolent look the other way policy of American armed forces.
But poppy cultivation and the heroin trade in Afghanistan does and the U.S.from the beginning did nothing to stop this cultivation but in fact maintained a virtually hands-off policy in order to "pacify" the war lords, drug lords and the smugglers known as the Northern Alliance with whom the U.S. formed an alliance to get alQueda and the Taliban. Needless to say Bush & Co's plan to play ball with the drug smugglers and farmers really pissed off Britain but Blair couldn't do anything about it. Everytime Blair brought it up in public with Bush standing nearby Bush just ignored him and didn't say a word.
Everytime Bush's original Director of the DEA (Asa Hutchinson) brought it up it was quickly quashed. He was finally replaced by a DEA director who played well with the administration. Asa Hutchinson was transferred to the DHS as an Administrator in charge of Transportation and Border Security in 2003.
Now that NATO is there this might change. Then again it might not. Afghanistan went from practically no poppy cultivation under Taliban rule to the world's largest supplier of heroin under Karzi and U.S. occupation. And the the local profits from this trade find their way to Taliban coffers and for terrorism operations including alQueda.
I don't get Congress completely ignoring this but so far they have.
Here's a recent (Mar 2007) UN report on the problem and it is a problem:
http://www.un.org/apps/news/story.asp?NewsID=21752&Cr=afghan&Cr1=
You can't make this stuff up. I wonder how many of our troops returned from Afghanistan hooked on heroin which is cheap and plentiful in the country thanks to the unholy alliance between the Bush administration and the drug dealers.