According to my hosting company, this attack is "ongoing". It is coming in waves and besides just messing with wordpress, this is tantamount to a DDOS attack and is holding up other traffic, even to your html sites. Sunday morning the attack lessened and sales became brisk, but it picked up heavy by noon and blasted servers all day. People sat on pages that took way too long to load so they bailed.
Can't say it's much worse than Googlebot who has also been hammering our server, accounting for over 50% of today's traffic.