Yes, that example takes time exponential in the number of blanks to (fail to) match - each time you add a blank to `input`, it essentially doubles the time required.

It's _possible_ for an implementation to deduce that `(\s+)+` is an insanely inefficient way to spell `\s+`, like it's _possible_ for an implementation to deduce that 10**10**10 - 10**10**10 is an insanely inefficient way to spell 0.

Python's does not.  To understand what's going on, Friedl's book "Mastering Regular Expressions" is an excellent source.