The Republican Party impeached Bill Clinton because he lied under oath about having sex with a White House intern. That was a pretty low bar for impeachment. Lawrence Tribe is a professor of constitutional law at Harvard. He argues that Donald Trump has admitted to obstructing justice even though he does not know enough about the Constitution to realize what he admitted. Republican's defended Richard Nixon when he faced impeachment for a serious crime. They gave up on their defense when Nixon, and officials in his administration, made things worse during the investigation of his crimes. Evidence of Nixon's behavior became available when secret tapes were discovered. Republican leaders told Nixon that he had lost their support and that he would be impeached. Nixon decided to resign in order to avoid impeachment.
Lawrence Tribe's argument is based upon his definition of the obstruction of justice. He claims that Trump's firing of the FBI is a clear example of the obstruction of justice. Trump also violated the law when he asked the FBI director to tell him the status of an ongoing investigation in which he and his campaign were potential targets. He also may be guilty of demanding loyalty from the FBI director who he invited to dinner in the Oval Office (Trump claims that Comey invited himself to plea for being retained in his job).
The Republican leadership will not impeach Trump because a constitutional lawyer from Harvard has accused Trump of obstructing justice. They realize that Trump's supporters could care less about how a Harvard law professor defines the obstruction of justice. Clinton's lie about having sex with an intern is another matter. The public understands what that is.
The ongoing investigation into the relationship between Trump's campaign associates and Russian interference in the US election will continue. Trump will obviously attempt to replace Comey with a loyalist. They are easy to find. For example, the senator from Texas demonstrated his loyalty during a Senate public hearing by accusing Sally Yates of wrongly refusing to defend a Trump order that she believed to be unlawful. He also made an effort to shift the discussion in the hearing from the Russian investigation to the issue that Trump wants to be investigated. That is, leaks from government officials to the press. He is one of the candidates on Trump's short list.