On Sunday, President Trump tweeted about Secretary of State Rex Tillerson, calling his efforts to negotiate with North Korea regarding the nuclear program "a Waste Of Time" -- according to Bloomberg. During his visit to Bejing, Tillerson told reporters that the U.S. has open communication channels with North Korea. Trump (again) sarcastically called Kim Jong-un a "Little Rocket Man" in his Sunday tweet.

Trump's tweet came a day after Tillerson's acknowledgment that the U.S. is probing North Korea. Trump said that Tillerson should save his energy in his second tweet on Sunday. It is unclear what he meant by "what has to be done."

Trump insulted the former presidents

Later, in a series of tweets, Trump insulted former U.S. presidents, saying Bill Clinton, George Bush, and Barak Obama failed to control North Korea's nonstop missile and nuclear tests.

He added that being nice to Rocket Man (Kim Jong-un) hasn't been working for 25 years. He showed the confidence that he would not fail in taking down Kim's efforts, BBC reported.

During the Obama administration, Kim became the leader of the DPRK in 2011, succeeding his father Kim Jong II. Former Presidents tried to negotiate with Pyongyang but failed in pressing the regime against conducting the nuclear programs

Trump's attitude towards N. Korea is totally different from Tillerson's. The war of words between the DPRK and President Trump showed that Trump was not afraid of Kim's threats and even threatened to destroy the regime. Anyway, Tillerson stated that military power would not solve the issue. He seemed to press North Korea economically by using the UN sanctions and urging countries not to accept workers from North Korea and stop funding the regime.

Tillerson's visit to Bejing

Heather Nauert, a spokeswoman for the U.S. State Department, said that the diplomatic channels for Kim would not be open forever. R.C. Hammond, a spokesman for Tillerson, said in Trump's support that he sent a clear message to N. Korea to appear at the negotiating table before the invitation became cold, according to Reuters.

China is the closest trading partner for the North, so Tillerson's main aim to visit Bejing was to press China to stop trading with the isolated regime and bring Kim to the negotiating table. Last week, China ordered North Korea to stop operating businesses on its territory after the United Nations imposed sanctions against the DPRK.