PayPal reports that an issue is currently affecting checkouts both on the PayPal site and their backend APIs which handle card-based payment authorizations -- indeed, at the moment it appears PayPal account login attempts are stalling out. We'll followup here once they report the issue is resolved.
https://www.paypal-notify.com/eventnotification/event
details_popup?eventId=7443Major Impact to PayPal APIs and PayPal Website
Live Site Status Update
Notification: We are experiencing a system issue which may be affecting PayPal APIs and PayPal Website on the PayPal Live Site. We will send an update with additional details within the next 15-30 minutes.
Sent Aug 24, 2016 05:52 PM MST by STC
Start time: Aug 24, 2016 05:44 PM MST
At this time, there is no alternative work-around.
Questions? Please contact PayPal Merchant Technical Services by filing a ticket; refer to PP-LIVE-7443