Here's what to know about the State of the UnionPresident Joe Biden will deliver his fourth State of the Union address tonight at 9 p.m. ET.The annual speech carries extra significance in an election year and it comes just days after Biden and former President Donald Trump appeared to lock up their respective party's nominations, setting them up for a rematch in November.Biden will speak in the House chamber before Congress where he's likely to face some heckling from Republicans and cheers from Democrats. Some Supreme Court justices typically attend as well.Members of Congress often send messages with the guests they invite. Tonight's guests include family members of hostages held by Hamas, the parents of a journalist held in Russia and people with personal experiences with abortion and IVF.Republican Sen. Katie Britt of Alabama will deliver the GOP response after Biden finishes his speech.