The impeachment of Donald Trump seems possible in 2019 IF the Democrats gain control of the House of Representatives, which seems highly likely, based upon polls 100 days out, and with the reminder that the party out of the White House always gains seats in the midterm elections, with the exceptions of 1934 under Franklin D. Roosevelt and 2002 under George W. Bush.
Having said that, it is reality that impeachment does not lead to convictions and removals from office, with the exception of seven federal district court judges over the long span of American history.
Richard Nixon would have been an exception if he had not resigned, but Andrew Johnson and Bill Clinton both were found not guilty in their impeachment trials.
Other Presidents have been threatened with impeachment, but it was more just a threat or simply could not gain enough support in the House of Representatives to lead to impeachment.
That list of threatened impeachments include: John Tyler in 1842 and 1843; James Buchanan in 1860; Ulysses S. Grant in 1876; Herbert Hoover in 1933; Harry Truman in 1951; Ronald Reagan in 1987; George H. W. Bush in 1991; George W. Bush in 2008; Barack Obama in 2013: and Donald Trump in 2017 and 2018. Notice most of these were not serious, and in many cases occurred in the last year of the President’s term or near the end of his last term in office.
Vice Presidents who have faced impeachment threats are: Schuyler Colfax in 1873, as he was leaving the Grant Administration; Spiro Agnew in 1973 as he neared resignation due to scandal under the Nixon Administration; George H. W. Bush in 1987 as the Iran Contra scandal emerged; and Dick Cheney in 2007 as the second Bush Administration dealt with the Iraq War continuation. None of them gained any traction.
Impeachment motions against Cabinet officers and other federal officials have been mostly just a gesture, a threat, as with, for example, Attorney General Eric Holder in 2013; Attorney General Alberto Gonzalez in 2007; and Secretary of Defense Donald Rumsfeld in 2004. Most recently threatened with impeachment is Deputy Attorney General Rod Rosenstein in the past few days, but unlikely to gain any traction, more used as a political ploy.