Tim Walz is expected to campaign without Democratic presidential nominee Kamala Harris this week as he addresses a firefighters union that has hundreds of thousands of members — and hasn’t yet endorsed a candidate for president. Harris’ running mate is expected to speak Wednesday at a convention for the International Association of Firefighters in Boston, NBC News reported. The union endorsed Joe Biden in 2020 but has not endorsed a candidate yet in 2024, according to the report. Organization President Edward Kelly told members leaders would make an endorsement only after surveying members abo…