Let me explain that to you again.
He did not call Roberts “the best ever”. He supported the nomination after it was made, but he had advocated for a different candidate, Michael Luttig. Luttig would have been a fine justice and, I suspect, woudl be President Cruz’s first Supreme Court nominee.
Roberts had been involved, along with Cruz and others, in Bush v. Gore and had done an outstanding job for them. That was how Cruz knew him, and based on that, he supported Roberts’s nomination — as did most conservatives (a notable exception being Ann Coulter).
That doesn’t make him, or them, or anyone but the person who nominated him (GW BUSH) and the Senators who voted to confirm him responsible for Roberts.
This is simply a bogus charge by Trump, and I think he knows it. (If he doesn’t, it says something about him that isn’t good.)
"Cruz went on to call Roberts "one of the very best advocates ever," who exemplified "how to try to carry out our craft with the highest level of skill and integrity." In that same message, dated Sept. 13, 2005, Cruz called Roberts "the best Supreme Court litigator in the nation." "I've worked with John and seen him argue numerous cases, and, to my mind, there's not another appellate advocate who's even close," he said... calling him [Roberts] "brilliant." In that article, Cruz explained that he had been part of the team that assembled lawyers to litigate Bush v. Gore, the case that decided the 2000 presidential election. Cruz wrote that he called Roberts and asked him to help with the team, and Roberts immediately hopped on a plane to Florida. "As an individual, John Roberts is undoubtedly a principled conservative, as is the president who appointed him," Cruz wrote in that op-ed.