diff --git a/src/govoplan_campaign/backend/manifest.py b/src/govoplan_campaign/backend/manifest.py
index 83107ae..8dcf8a3 100644
--- a/src/govoplan_campaign/backend/manifest.py
+++ b/src/govoplan_campaign/backend/manifest.py
@@ -669,7 +669,9 @@ manifest = ModuleManifest(
                 "and ownership-transfer records describe governance visibility separately from the content grant. Saved imports expose "
                 "only their stable source identity and revision, while independently user-owned mapping profiles never inherit a Campaign "
                 "share. Persisted validation, build, snapshot, and review artifacts use typed version references. Reusable templates and "
-                "durable export packages stay with their optional owning modules and fail closed when Campaign is asked to explain them."
+                "durable export packages stay with their optional owning modules and fail closed when Campaign is asked to explain them. "
+                "The shared explanation dialog evaluates the signed-in user by default. Policy may permit a tenant-bounded selected-user "
+                "administrator diagnostic; Access returns only permitted subject metadata and records every cross-user explanation in audit evidence."
             ),
             layer="available",
             documentation_types=("admin",),
@@ -693,7 +695,7 @@ manifest = ModuleManifest(
                     kind="repository",
                 ),
             ),
-            related_modules=("access", "mail", "postbox", "templates"),
+            related_modules=("access", "audit", "mail", "policy", "postbox", "templates"),
             translations={
                 "de": {
                     "title": "Zugriff auf untergeordnete Campaign-Nachweise erklaeren",
diff --git a/webui/src/api/campaigns.ts b/webui/src/api/campaigns.ts
index 1bcb53a..6a4cd43 100644
--- a/webui/src/api/campaigns.ts
+++ b/webui/src/api/campaigns.ts
@@ -5,11 +5,15 @@ import {
   type ReferenceOptionProvider
 } from "@govoplan/core-webui";
 import { campaignJobsQueryParams, type CampaignJobsQueryParameters } from "../features/campaigns/utils/jobListQuery";
-export { fetchResourceAccessExplanation } from "@govoplan/core-webui";
+export {
+  fetchResourceAccessExplanation,
+  fetchResourceAccessExplanationSubjects
+} from "@govoplan/core-webui";
 export type {
   AccessDecisionProvenanceItem,
   ResourceAccessExplanationUser as AccessExplanationUser,
-  ResourceAccessExplanationResponse
+  ResourceAccessExplanationResponse,
+  ResourceAccessExplanationSubjectsResponse
 } from "@govoplan/core-webui";
 
 export type CampaignListResponse =
diff --git a/webui/src/features/campaigns/components/CampaignAccessCard.tsx b/webui/src/features/campaigns/components/CampaignAccessCard.tsx
index 824e4d8..9035f0d 100644
--- a/webui/src/features/campaigns/components/CampaignAccessCard.tsx
+++ b/webui/src/features/campaigns/components/CampaignAccessCard.tsx
@@ -9,12 +9,14 @@ import {
 } from "lucide-react";
 import {
   fetchResourceAccessExplanation,
+  fetchResourceAccessExplanationSubjects,
   getCampaignShares,
   campaignShareTargetProvider,
   revokeCampaignShare,
   upsertCampaignShare,
   type CampaignShare,
-  type ResourceAccessExplanationResponse } from
+  type ResourceAccessExplanationResponse,
+  type ResourceAccessExplanationSubjectsResponse } from
 "../../../api/campaigns";
 import {
   Button,
@@ -72,6 +74,8 @@ export default function CampaignAccessCard({
   const [sharePermission, setSharePermission] = useState<"read" | "write">("read");
   const [accessExplanationOpen, setAccessExplanationOpen] = useState(false);
   const [accessExplanation, setAccessExplanation] = useState<ResourceAccessExplanationResponse | null>(null);
+  const [accessExplanationSubjects, setAccessExplanationSubjects] = useState<ResourceAccessExplanationSubjectsResponse | null>(null);
+  const [accessExplanationSubjectId, setAccessExplanationSubjectId] = useState("");
   const [accessExplanationLoading, setAccessExplanationLoading] = useState(false);
   const [ownershipTransfers, setOwnershipTransfers] = useState<OwnershipTransfer[]>([]);
   const [busy, setBusy] = useState(false);
@@ -346,13 +350,24 @@ export default function CampaignAccessCard({
   }
 
   async function openAccessExplanation() {
-    if (!auth.user?.id) return;
+    const currentUserId = auth.principal?.membership_id || auth.user?.id;
+    if (!currentUserId) return;
     setAccessExplanationOpen(true);
     setAccessExplanation(null);
+    setAccessExplanationSubjects(null);
     setAccessExplanationLoading(true);
     try {
+      const subjects = await fetchResourceAccessExplanationSubjects(settings, {
+        tenantId: (auth.active_tenant ?? auth.tenant)?.id
+      });
+      const initialSubjectId = subjects.users.some((user) => user.id === currentUserId)
+        ? currentUserId
+        : subjects.users[0]?.id;
+      if (!initialSubjectId) throw new Error("No permitted access-explanation subject is available.");
+      setAccessExplanationSubjects(subjects);
+      setAccessExplanationSubjectId(initialSubjectId);
       setAccessExplanation(await fetchResourceAccessExplanation(settings, {
-        userId: auth.user.id,
+        userId: initialSubjectId,
         resourceType: "campaign",
         resourceId: campaign.id,
         action: "campaigns:campaign:read",
@@ -366,6 +381,26 @@ export default function CampaignAccessCard({
     }
   }
 
+  async function selectAccessExplanationSubject(userId: string) {
+    if (userId === accessExplanationSubjectId) return;
+    setAccessExplanationLoading(true);
+    try {
+      const explanation = await fetchResourceAccessExplanation(settings, {
+        userId,
+        resourceType: "campaign",
+        resourceId: campaign.id,
+        action: "campaigns:campaign:read",
+        tenantId: (auth.active_tenant ?? auth.tenant)?.id
+      });
+      setAccessExplanation(explanation);
+      setAccessExplanationSubjectId(userId);
+    } catch (err) {
+      onError(err instanceof Error ? err.message : String(err));
+    } finally {
+      setAccessExplanationLoading(false);
+    }
+  }
+
   const columns = useMemo<DataGridColumn<CampaignShare>[]>(() => [
   {
     id: "target",
@@ -517,8 +552,15 @@ export default function CampaignAccessCard({
         <FormField label="i18n:govoplan-campaign.access.2f81a22d"><select value={sharePermission} onChange={(event) => setSharePermission(event.target.value as "read" | "write")}><option value="read">i18n:govoplan-campaign.can_view.1b3e4006</option><option value="write">i18n:govoplan-campaign.can_edit_and_operate.77acb15e</option></select></FormField>
       </Dialog>
 
-      <Dialog open={accessExplanationOpen} className="campaign-access-dialog" title="i18n:govoplan-core.access_explanation.75ee7f62" onClose={() => { if (!accessExplanationLoading) { setAccessExplanationOpen(false); setAccessExplanation(null); } }} footer={<Button onClick={() => { setAccessExplanationOpen(false); setAccessExplanation(null); }} disabled={accessExplanationLoading}>i18n:govoplan-campaign.close.bbfa773e</Button>}>
-        <ResourceAccessExplanation loading={accessExplanationLoading} explanation={accessExplanation} fallbackResourceLabel={campaign.name || campaign.external_id || campaign.id} />
+      <Dialog open={accessExplanationOpen} className="campaign-access-dialog" title="i18n:govoplan-core.access_explanation.75ee7f62" onClose={() => { if (!accessExplanationLoading) { setAccessExplanationOpen(false); setAccessExplanation(null); setAccessExplanationSubjects(null); setAccessExplanationSubjectId(""); } }} footer={<Button onClick={() => { setAccessExplanationOpen(false); setAccessExplanation(null); setAccessExplanationSubjects(null); setAccessExplanationSubjectId(""); }} disabled={accessExplanationLoading}>i18n:govoplan-campaign.close.bbfa773e</Button>}>
+        <ResourceAccessExplanation
+          loading={accessExplanationLoading}
+          explanation={accessExplanation}
+          subjects={accessExplanationSubjects}
+          selectedUserId={accessExplanationSubjectId}
+          onSelectedUserIdChange={(userId) => void selectAccessExplanationSubject(userId)}
+          fallbackResourceLabel={campaign.name || campaign.external_id || campaign.id}
+        />
       </Dialog>
 
       <ConfirmDialog open={Boolean(revokeTarget)} title="i18n:govoplan-campaign.remove_campaign_share.2c2d42eb" message="i18n:govoplan-campaign.remove_this_user_s_or_group_s_explicit_access_to.5ff07672" confirmLabel="i18n:govoplan-campaign.remove_share.69c932e1" tone="danger" busy={busy} onCancel={() => setRevokeTarget(null)} onConfirm={() => void revoke()} />