Former President Barack Obama is angry with President Trump due to the tweets that accused the former president of ordering an illegal wiretap on his campaign. Obama did not return a phone call that President Trump made to Obama. President Trump was calling him to say thank you for a letter he left the new president in the resolute desk, as per tradition, following Trump’s inauguration. The pair initially seemed to have a good relationship and appeared to be friendly during the inauguration, with Obama even offering to help consult Trump on the presidency for the first few months so that he could adapt more smoothly with the pressure of being the POTUS. Then, on January 30th, Obama showed his support for anti-Trump protests and everything had been downhill since then.
From Washington Examiner:
The two presidents promised to have a good relationship and seemed at least outwardly chummy during the inauguration. Obama had even offered to consult for Trump on the presidency during his first months to help him deal with the pressures of the office. But, it appears that is now on hold and the traditional relationship between presidents is on the rocks. Usually, current presidents and ex-presidents show some deference to each other in order to uphold the decorum of the office.