diff -u b/src/Form/EntryForm.php b/src/Form/EntryForm.php
--- b/src/Form/EntryForm.php
+++ b/src/Form/EntryForm.php
@@ -147,18 +147,17 @@
       $form['#cache'] = ['max-age' => 0];
     }
 
-    // Get current validation plugin form.
+    // Instantiate the validation plugin.
     $this->tfaValidationPlugin = $this->tfaValidationManager->createInstance($validation_plugin, ['uid' => $user->id()]);
+    if ($this->tfaValidationPlugin instanceof TfaValidationSendInterface) {
+      $this->tfaValidationManager->begin($validation_plugin);
+    }
+    // Get current validation plugin form.
     $form = $this->tfaValidationPlugin->getForm($form, $form_state);
 
+    // Get the re-send button if one exists.
     if ($this->tfaValidationPlugin instanceof TfaValidationSendInterface) {
-      $sent = $this->getRequest()->getSession()->get('validation_plugin_begin');
-
-      if (empty($sent[$validation_plugin])) {
-        $this->tfaValidationPlugin->begin();
-        $sent[$validation_plugin] = 1;
-        $this->getRequest()->getSession()->set('validation_plugin_begin', $sent);
-      }
+      // @TODO Consider how best to add the re-send button.
     }
 
     $this->tfaLoginPlugins = $this->tfaLoginManager->getPlugins(['uid' => $user->id()]);
@@ -287,7 +286,6 @@
 
     // TODO Should finalize() be after user_login_finalize or before?!
     // TODO This could be improved with EventDispatcher.
-    $this->getRequest()->getSession()->remove('validation_plugin_begin');
     $this->finalize();
     $this->flood->clear('tfa.failed_validation', $this->floodIdentifier);
     $form_state->setRedirect('<front>');
diff -u b/src/Form/TfaLoginForm.php b/src/Form/TfaLoginForm.php
--- b/src/Form/TfaLoginForm.php
+++ b/src/Form/TfaLoginForm.php
@@ -8,6 +8,7 @@
 use Drupal\Core\Render\RendererInterface;
 use Drupal\Core\Routing\RedirectDestinationInterface;
 use Drupal\Core\Url;
+use Drupal\tfa\Plugin\TfaValidationSendInterface;
 use Drupal\tfa\TfaContext;
 use Drupal\tfa\TfaDataTrait;
 use Drupal\tfa\TfaLoginTrait;
@@ -174,6 +175,15 @@
       return parent::submitForm($form, $form_state);
     }
 
+    // Instantiate the validation plugins.
+    $validation_plugin_definitions = $this->tfaValidationManager->getDefinitions();
+    foreach ($validation_plugin_definitions as $plugin_id => $plugin_definition) {
+      $plugin_instance = $this->tfaValidationManager->createInstance($plugin_definition, ['uid' => $user->id()]);
+      if ($plugin_instance instanceof TfaValidationSendInterface) {
+        $this->tfaValidationManager->reset($plugin_instance);
+      }
+    }
+
     // Setup TFA.
     if ($this->tfaContext->isReady()) {
       $this->loginWithTfa($form_state);
reverted:
--- b/src/Plugin/TfaValidationSendInterface.php
+++ /dev/null
@@ -1,20 +0,0 @@
-<?php
-
-namespace Drupal\tfa\Plugin;
-
-/**
- * Interface TfaValidationSendInterface.
- *
- * Validation plugins that implement this interface are able to interact with
- * the Tfa begin() process to communicate a code during the start of the TFA
- * process.
- */
-interface TfaValidationSendInterface {
-
-  /**
-   * TFA process begin. If the plugin needs to deliver a validation code, this
-   * is the ideal place to perform that delivery.
-   */
-  public function begin();
-
-}
reverted:
--- b/tests/modules/tfa_test_plugins/src/Plugin/TfaSetup/TfaTestValidationSendPluginSetupPlugin.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php
-
-namespace Drupal\tfa_test_plugins\Plugin\TfaSetup;
-
-/**
- * Class TfaTestValidationPluginSetupPlugin.
- *
- * @package Drupal\tfa_test_plugins
- *
- * @TfaSetup(
- *   id = "tfa_test_plugins_validation_send_setup",
- *   label = @Translation("TFA Test Validation Send Plugin Setup"),
- *   description = @Translation("Setup plugin for the validation plugin that implements the TfaValidationSend interface."),
- *   helpLinks = {},
- *   setupMessages = {}
- * )
- */
-class TfaTestValidationSendPluginSetupPlugin extends TfaTestValidationPluginSetupPlugin {}
reverted:
--- b/tests/modules/tfa_test_plugins/src/Plugin/TfaValidation/TfaTestValidationSendPlugin.php
+++ /dev/null
@@ -1,47 +0,0 @@
-<?php
-
-namespace Drupal\tfa_test_plugins\Plugin\TfaValidation;
-
-use Drupal\Core\Form\FormStateInterface;
-use Drupal\tfa\Plugin\TfaBasePlugin;
-use Drupal\tfa\Plugin\TfaValidationInterface;
-use Drupal\tfa\Plugin\TfaValidationSendInterface;
-
-/**
- * Class for testing the sending API.
- *
- * @TfaValidation(
- *   id = "tfa_test_plugins_validation_send",
- *   label = @Translation("Test Validation Send Plugin"),
- *   description = @Translation("Test Validation Plugin that implements the TfaValidationSend interface"),
- * )
- */
-class TfaTestValidationSendPlugin extends TfaBasePlugin implements TfaValidationInterface, TfaValidationSendInterface {
-
-  /**
-   * {@inheritdoc}
-   */
-  public function begin() {}
-
-  /**
-   * {@inheritdoc}
-   */
-  public function ready() {
-    return TRUE;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getForm(array $form, FormStateInterface $form_state) {
-    return $form;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function validateForm(array $form, FormStateInterface $form_state) {
-    return TRUE;
-  }
-
-}
only in patch2:
unchanged:
--- a/src/TfaValidationPluginManager.php
+++ b/src/TfaValidationPluginManager.php
@@ -7,9 +7,12 @@ use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Plugin\DefaultPluginManager;
+use Drupal\Core\TempStore\PrivateTempStore;
 use Drupal\encrypt\EncryptionProfileManagerInterface;
 use Drupal\encrypt\EncryptService;
 use Drupal\encrypt\EncryptServiceInterface;
+use Drupal\tfa\Plugin\TfaValidationInterface;
+use Drupal\tfa\Plugin\TfaValidationSendInterface;
 use Drupal\user\UserDataInterface;
 
 /**
@@ -17,6 +20,11 @@ use Drupal\user\UserDataInterface;
  */
 class TfaValidationPluginManager extends DefaultPluginManager {
 
+  /**
+   * The prefix for recording whether a validation plugin has been initiated.
+   */
+  const VALIDATION_BEGIN = 'tfa_validation_begun';
+
   /**
    * Provides the user data service object.
    *
@@ -38,6 +46,13 @@ class TfaValidationPluginManager extends DefaultPluginManager {
    */
   protected $encryptService;
 
+  /**
+   * Private Temporary Storage service
+   *
+   * @var \Drupal\Core\TempStore\PrivateTempStore
+   */
+  protected $tempStore;
+
   /**
    * Constructs a new TfaValidation plugin manager.
    *
@@ -56,13 +71,16 @@ class TfaValidationPluginManager extends DefaultPluginManager {
    *   Encryption profile manager.
    * @param \Drupal\encrypt\EncryptServiceInterface $encrypt_service
    *   Encryption service.
+   * @param \Drupal\encrypt\EncryptServiceInterface $encrypt_service
+   *   Private temporary storage service.
    */
-  public function __construct(\Traversable $namespaces, CacheBackendInterface $cache_backend, ModuleHandlerInterface $module_handler, ConfigFactoryInterface $config_factory, UserDataInterface $user_data, EncryptionProfileManagerInterface $encryption_profile_manager, EncryptServiceInterface $encrypt_service) {
+  public function __construct(\Traversable $namespaces, CacheBackendInterface $cache_backend, ModuleHandlerInterface $module_handler, ConfigFactoryInterface $config_factory, UserDataInterface $user_data, EncryptionProfileManagerInterface $encryption_profile_manager, EncryptServiceInterface $encrypt_service, PrivateTempStore $temp_store) {
     parent::__construct('Plugin/TfaValidation', $namespaces, $module_handler, 'Drupal\tfa\Plugin\TfaValidationInterface', 'Drupal\tfa\Annotation\TfaValidation');
     $this->alterInfo('tfa_validation');
     $this->setCacheBackend($cache_backend, 'tfa_validation');
     $this->userData = $user_data;
     $this->encryptService = $encrypt_service;
+    $this->tempStore = $temp_store;
     $this->encryptionProfileManager = $encryption_profile_manager;
   }
 
@@ -91,4 +109,46 @@ class TfaValidationPluginManager extends DefaultPluginManager {
     return $plugin;
   }
 
+  /**
+   * Returns the key used to record whether the plugin needs to be initiated.
+   *
+   * @param \Drupal\tfa\Plugin\TfaValidationSendInterface $validation_plugin
+   *   The validation plugin being initiated.
+   *
+   * @return string
+   */
+  protected function getInitiationKey(TfaValidationSendInterface $validation_plugin) {
+    return implode(':', [self::VALIDATION_BEGIN, $validation_plugin->getPluginId()]);
+  }
+
+  /**
+   * Initiate any functionality that needs to run when the plugin is first
+   * loaded, and mark the plugin as begun.
+   *
+   * @param \Drupal\tfa\Plugin\TfaValidationSendInterface $validation_plugin
+   *   The validation plugin being initiated.
+   */
+  public function begin(TfaValidationSendInterface $validation_plugin) {
+    if ($this->tempStore->get($this->getInitiationKey($validation_plugin))) {
+      $validation_plugin->begin();
+
+      // Mark this plugin as initiated.
+      $this->tempStore->set($this->getInitiationKey($validation_plugin), FALSE);
+    }
+  }
+
+  /**
+   * Mark the validation plugin as ready to begin.
+   *
+   * @param \Drupal\tfa\Plugin\TfaValidationSendInterface $validation_plugin
+   *   The validation plugin being reset.
+   */
+  public function reset(TfaValidationSendInterface $validation_plugin) {
+    if (!method_exists($validation_plugin, 'begin')) {
+      return;
+    }
+
+    $this->tempStore->set($this->getInitiationKey($validation_plugin), TRUE);
+  }
+
 }