bastards just came into my house to arrest a family member who lives with me, threatened to gas the place out when we asked for a warrant, repeatedly lied to a less cop-wary house member, and stormed into their target's room (while they were sleeping after a night shift!) and dragged them out without anything else to say except "you can bail them out for $300,000 :^)"
AND YOU KNOW WHAT THEY'RE WANTED FOR?
A CAR CRASH A YEAR AGO 
THANKS FOR FUCKING OVER THEIR LIFE RIGHT AS IT WAS TURNING AROUND FOR THE BETTER
Yes i am amerikkkan how could you tell. Death to the police state, death to amerikkka
Not sure if this is a serious question or not, but nope, they don't for most civilian homes. Things can vary slightly depending on the the state or municipality, but the moment you open the door for them they are legally permitted to be inside. The legal bar is really low to manufacture pretext for anything else they want from that point forward. Cops can lie through their teeth and say whatever they want to get you to open the door and will threaten every aspect of your life in the process usually.
Warrants are generally only used when they want legal permission to bust the door down or if the person has some sort of legal, capital, or political influence.
That sounds so scary and crazy AF. Like I know it is bad with cops in the US but never have been there and it sounds worse the more you learn.