What actions would count as "serious attempt":
Congressional Action:

• Introduction of formal legislation in Congress to declare Mamdani ineligible under Section 3 of the 14th Amendment

• A congressional vote on declaring Mamdani ineligible

• Speaker Mike Johnson formally placing such a measure on the House agenda

Court Filing:

• Filing a federal lawsuit invoking Section 3 of the 14th Amendment to prevent Mamdani from taking office

• Any official legal challenge filed by House Republicans, the New York Young Republican Club, or allied groups

Just talking about it in interviews or on social media does NOT count

Context: https://thehill.com/homenews/state-watch/5412579-insurrection-clause-mamdani-mayor/