Considered an inter-discipline that is associated with the study of the linguistic relationship of power and ideology, critical discourse analysis (CDA) attracts more and more attention to be easily applied to analyze linguistic features through some certain social and cultural background. CDA is built upon Halliday's systemic functional grammar (SFG) that is considered to be a practical method to analyze discourse. As a kind of typical discourse combining the speaker's ideology and intention, political discourse can be analyzed by CDA. Accordingly, this research analyzes Donald Trump's, the ex-American president, speech about Al-Baghdady mainly from the perspectives of transitivity and modality with the aim of revealing the speaker's political intention. The research concludes that Trump uses different linguistic alternations to transmit, change, and retain audiences' ideologies. Further, it attains a positive impact upon the CDA's development.Everyone takes a lot of precautions in choosing the most appropriate sentence structures in addition to certain lexemes so as to win some favorite responses. Despite their distinctive positions, politicians make no exceptions. Speech-makers have a well-built command of linguistic manipulation skills so as to have some persuasive choices for moving the public to accept and advocate such related policies. In contrast, dictators are those persons who take mostly advantage of this in order to encode skill effectively to path a legal track for their government.