The Trinity ( in regards to Jesus) is best described in this two passages from Paul:
Philippians 2:5-11
New American Standard Bible (NASB)
5 Have this attitude in yourselves which was also in Christ Jesus, 6 who, although He existed in the form of God, did not regard equality with God a thing to be grasped, 7 but emptied Himself, taking the form of a bond-servant, and being made in the likeness of men. 8 Being found in appearance as a man, He humbled Himself by becoming obedient to the point of death, even death on a cross. 9 For this reason also, God highly exalted Him, and bestowed on Him the name which is above every name, 10 so that at the name of Jesus every knee will bow, of those who are in heaven and on earth and under the earth, 11 and that every tongue will confess that Jesus Christ is Lord, to the glory of God the Father.
Colossians 2:9-15
New American Standard Bible (NASB)
9 For in Him all the fullness of Deity dwells in bodily form, 10 and in Him you have been made complete, and He is the head over all rule and authority; 11 and in Him you were also circumcised with a circumcision made without hands, in the removal of the body of the flesh by the circumcision of Christ; 12 having been buried with Him in baptism, in which you were also raised up with Him through faith in the working of God, who raised Him from the dead. 13 When you were dead in your transgressions and the uncircumcision of your flesh, He made you alive together with Him, having forgiven us all our transgressions, 14 having canceled out the certificate of debt consisting of decrees against us, which was hostile to us; and He has taken it out of the way, having nailed it to the cross. 15 When He had disarmed the rulers and authorities, He made a public display of them, having triumphed over them through Him.
Jesus has the same Nature as The Father and, just like a human son who shares his human nature with his father, Christ shares His Divine Nature with His Father and, if His Father is God ( A statement of Whoi and WHat the Father is, not a name), then Chris is God.
The only people that have issues with the Trinity doctrine are those that associate the word God with the PERSONAL identity of The Father of Christ.
To them, God = The Father ( another name, sole title, etc) so to claim that Christ was God is, to them, to claim that Christ is His Own Father.