Robert F. Kennedy Jr. is doubling down on his support for an executive order that would aim to boost the production of a controversial weedkiller ingredient called glyphosate, even though it is widening a political fault line for the administration ahead of the midterm elections.

MAHA activists who want to hold corporations accountable for harming Americans’ health have found an unlikely ally in a Republican-led Environmental Protection Agency that has traditionally supported big businesses and less regulation.