ABU DHABI, United Arab Emirates ó Former President George W. Bush said on Thursday that "thereís pretty clear evidence that the Russians meddled" in the 2016 American presidential election, forcefully rebutting fellow Republican Donald Trumpís denials of Moscow trying to affect the vote. While never mentioning President Trump by name, Bush appeared to be pushing back on Trumpís attempts to have warmer relations with Russia, as well as his comments on immigration. The White House did not immediately comment on Bushís remarks. "Thereís pretty clear evidence that the Russians meddled," Bush said at a talk in Abu Dhabi, the capital of the United Arab Emirates. "Whether they affected the outcome is another question." Bush also said that "itís problematic that a foreign nation is involved in our election system. Our democracy is only as good as people trust the results." U.S. intelligence agencies have concluded Russia meddled in the 2016 election to help Trump win. Numerous investigations are under way to determine whether Trumpís campaign aided the Kremlin in its efforts. Trump has repeatedly denied any "collusion" with Russia. Speaking of Russian President Vladimir Putin, Bush called him "zero-sum." "Heís got a chip on his shoulder," Bush said of Putin. "The reason he does is because of the demise of the Soviet Union troubles him. Therefore, much of his moves (are) to regain Soviet hegemony." Bush also stressed the need to back NATO and other alliances the U.S. has with the world. Putin "is pushing, constantly pushing, probing weaknesses," the former president said. "Thatís why NATO is very important." Bush also criticized Trumpís decision to scrap a program implemented by former President Barack Obamaís administration that allows young immigrants living in the U.S. illegally who were brought here as children to remain in America. "Americaís their home," the 43rd American president said. "Theyíve got to get it fixed." Bush acknowledged that he tried to overhaul Americaís "broken" immigration system, but failed. "There are people willing to do jobs that Americans wonít do," he said. "Americans donít want to pick cotton at 105 degrees (Fahrenheit), but there are people who want put food on their familyís tables and are willing to do that. We ought to say thank you and welcome them." Bush in 2008 became the first sitting U.S. president to visit the UAE. He spoke Thursday at a summit in Abu Dhabi put on by the Milken Institute, an economic think tank based in California. He made his comments while in a conversation with Michael Milken, known as the king of high-risk "junk" bonds in the 1980s. Milken pleaded guilty to securities-law violations in 1990 and served 22 months in prison. He agreed in a settlement with the SEC to a lifetime ban from the securities industry and paid a $200 million fine. Milken, who is a prostate cancer survivor, and his family have given hundreds of millions of dollars away in recent decades. Forbes magazine estimates Milken, 71, is now worth some $3.6 billion.