President Bill Clinton is due to announce, by tomorrow, whether or not to "certify" the two nations as cooperating against narcotics production and trafficking. At stake are US aid, loans, future investments, tourism potential and, not least, simple national pride.
The certification process, under which the President is required by law to report to Congress on more than 30 drug-producing or transit countries, has come under increasing criticism this year, not only from the targeted countries but within the US itself.
Mexico calls it "interventionist", Colombia bills it "imperialist". A New York Times editorial this week said it should be abolished and that the US should clean up its own backyard by combating drug consumption. Even US anti-drugs tsar General Barry McCaffrey has questioned its usefulness.
The general has reason to be confused. His Mexican counterpart, whom he recently praised as exemplary, was jailed last week for his alleged links with a leading drug cartel. US intelligence agents are now extremely concerned as to how much information General Jesus Gutierrez Rebollo may have passed on to the druglords.
Latin American analysts warn that the certification policy is fanning a new anti-Americanism in the region and could lead to strained relations - particularly between neighbours Mexico and the US - and even to a new anti-American bloc.
Such sentiment could complicate Mr Clinton's plans to create a pan-American free trade zone by the year 2005 - a key reason for his upcoming Latin American tour, including Mexico, in April and May.
Colombian MPs are preparing a Bill that would allow reprisals against US interests if the country is "decertified" for the second straight year. The Colombian government has flooded the US media with a campaign listing its efforts against drug trafficking but despite these efforts, cocaine production was said to have gone up by 30 per cent last year, according to US officials.
Last year, Mr Clinton "decertified" Afghanistan, Burma, Nigeria, Iran, Syria and Colombia, where President Ernesto Samper narrowly escaped impeachment on charges he took election campaign funds from the Cali cocaine cartel. This year, for the first time, Mexico could be added to the list, though with a "national interests waiver" that would make the move largely symbolic, US officials say. Mexico would be reprimanded but with the waiver that it would not be in the US national interests to impose economic sanctions.
Jamaica and Belize could also be downgraded this year after an upsurge in the transit of marijuana and cocaine.
In addition to the arrest of its anti-drugs chief, Mexico has been shaken this month by allegations that the governors of two states, as well as former President Carlos Salinas's father, were linked to drug traffickers. All deny the charges.
Last year's "decertification" of Colombia delayed US aid and made it difficult for the country to attract new loans. This year, Mr Clinton may recommend added sanctions, such as refusing landing rights to Colombian aircraft, rescinding preferential tariffs on Colombian coffee and submitting Colombian citizens to onerous searches at US airports. Colombia, of course, would be likely to reciprocate.