Cannot redeclare class Drush error When I go to my site on command line and run a drush command I get the following error:

PHP Fatal error:  Cannot redeclare class Drush in /var/www/xmd8/www/vendor/drush/drush/lib/Drush.php on line 36


If I run which drush I get:

/usr/local/bin/drush


I have the Lightning Distribution installed via composer and they are adding Drush. 

Any ideas on how to fix this?
What version of Drush are you using?  Recent versions of Drush will notice that there is a copy of Drush included in your Drupal site, and will redispatch (exec) to use it instead.  If you are using an old, unsupported version of Drush (e.g. Drush 6 or earlier), then it will not do this, and the error you see above would be the likely result.