Summary: Wednesday on the NewsHour, smoke from Canadian wildfires blankets wide swaths of the eastern United States, causing air quality concerns for millions. Rescuers rush to get civilians to safety in Ukraine after a catastrophic dam breach floods streets and buildings. Plus, the GOP presidential field expands with former Vice President Mike Pence and North Dakota Gov. Doug Burgum announcing bids. PBS NewsHour is supported by - https://www.pbs.org/newshour/about/funders
