[Lurking Libertarian]

Is the challenge of eligibility by one congressman all it takes?

No. You need a minimum of one Congressman and one Senator to even make an objection. (The statute is quoted above in this thread.) If an objection is made, the Senate and the House then vote on whether to count the disputed Electoral Votes or not. A majority vote is sufficient to count EVs over an objection.

[Red_Devil 232]

Thanks. I looked it up to answer my question and posted the U.S. Code in #45.