I am trying to make a lead owner change approval process. I thought I was good with the code but nothing is triggering. Can anyone help?

trigger LeadReassignment on Lead (before update) {
    for (Lead obj: trigger.new){


        List<Lead> ld = [SELECT Id, OwnerID, Reassignment_Status__c FROM Lead WHERE Id IN :Trigger.old];

        List<ProcessInstance> pi = [SELECT SubmittedById,SystemModstamp,TargetObjectId, Status,  (SELECT ID, ProcessNodeId, StepStatus, Comments,TargetObjectId,ActorId,CreatedById,IsDeleted,IsPending, OriginalActorId,ProcessInstanceId,RemindersSent,CreatedDate 
        FROM StepsAndWorkitems ) FROM ProcessInstance pi WHERE pi.TargetObjectId IN :Trigger.old order by createddate DESC limit 1];


        If (ld[0].Reassignment_Status__c == 'Pending' && pi[0].Status == 'Approved') {
            obj.OwnerID = pi[0].SubmittedById;
            obj.Reassignment_Status__c = '';
            system.debug('Reassignment Approved - Owner Changed from '+ld[0].OwnerId+'to ' +pi[0].SubmittedById);
                                                        }

         If (ld[0].Reassignment_Status__c == 'Pending' && pi[0].Status == 'Rejected') {
            obj.Reassignment_Status__c = '';

            system.debug('Reassignment Rejected - Owner not changed');

                                                         }