to doubt

verb
  1. To feel uncertain about something or to lack confidence in something or someone. verb
    She began to doubt her own abilities after failing the test.
    He doubted whether the plan would succeed.
  2. To consider something unlikely or to suspect that something may not be true. verb
    I doubt that he will come to the party, as he is usually busy on weekends.
    They doubted the authenticity of the painting.