Mr Graham told reporters he was confident Mr Trump's legal team would rise above its performance on the trial's opening day, which many Republicans felt was lacklustre.
“I think his team will do better, can do better,” Mr Graham told reporters. “I reinforced to the president, the case is over. It’s just a matter of getting the final verdict now.”
Sources close to Mr Trump told CNN that the former president was furious about his team's performance on the first day of the trial.
Mr Trump reportedly vented at his television while watching Bruce Castor's remarks. He was apparently more accepting of attorney David Schoen's comments.
Mr Castor even admitted that the Trump defence team adjusted their opening remarks because the Democrats' video was so powerful.
"I'll be quite frank with you," Mr Castor said. "We changed what we were going to do on account that we thought that the House managers' presentation was well done."
He went on to call the Democrats presenting that day "brilliant speakers" who he "loved listening to".
The former president's advisers reportedly told him that his history of not paying workers and insistence on basing arguments on false and debunked information likely contributed to the lacklustre state of his defence team.
Mr Graham said he reassured Mr Trump that he would be acquitted, and said that the president was not especially frustrated when the two men spoke.
At the same time, Mr Trump's legal team scrambled to pull together videos to use in its defence of the former president.
The Democratic impeachment managers opened the trial with a video compiling the violence and hatred on display during the Capitol insurrection.
According to a person familiar with the situation, Mr Trump's team is trying to quickly pull together something similar to use in defence of the former president.
The source, who spoke with CNN, claimed that the Republican video would feature Democrats who did not immediately concede their elections.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies