If your perforce server is more secure, it only accepts ticket based authentication. Unfortunately, the Jenkins perforce plugin appears to have issues in this regard. Judging from the output, the commands generated are correct, but there is something that is amiss.

Build output snippet:
[test] $ /auto/perforce/p4bin/p4 login -a -p
[test] $ /auto/perforce/p4bin/p4 -P 618EXXXXXXXXXXXXXXXXBB180 workspace -o cmayeux:condor-main-js-ut-exp3-912254826

Running these exact commands on the slave outside of Jenkins yields the desired result. However, in the plugin, I get the following output:

Caught exception communicating with perforce. Perforce password (P4PASSWD) invalid or unset.com.tek42.perforce.PerforceException: Perforce password (P4PASSWD) invalid or unset.
at com.tek42.perforce.parse.AbstractPerforceTemplate.getPerforceResponse(AbstractPerforceTemplate.java:406)
at com.tek42.perforce.parse.AbstractPerforceTemplate.getPerforceResponse(AbstractPerforceTemplate.java:301)
at com.tek42.perforce.parse.Workspaces.getWorkspace(Workspaces.java:61)
at hudson.plugins.perforce.PerforceSCM.getPerforceWorkspace(PerforceSCM.java:1615)
...

Not sure what exactly is going wrong. I've verified my password six ways to Sunday. Note this only occurs when perforce is secured so as to not allow environment variables or .p4configs be used for the P4PASSWD.