Wednesday on the NewsHour, President Biden and former President Trump agree to debate as primary results offer a fresh glimpse into voters' minds. Ukrainian President Zelenskyy pleads for more weapons as Russian forces advance in the northeast. Plus, a look at the transmission of bird flu to cows and why scientists are concerned we're not watching the virus' spread closely enough. PBS NewsHour is supported by - https://www.pbs.org/newshour/about/funders