Are democrats persecuting Trump in an unfair way?  Well, the republicans did not try to impeach Obama.  They, however, talked about it. A lot.

• In 2010, Rep. Darrell Issa said Obamacould face impeachment after Rep. Joe Sestak claimed the White House offered him a job to prevent him from challenging Arlen Specter in a primary.
• In 2011, Rep. Michael Burgess told a local Tea Party groupthat Obama’s impeachment “needs to happen,” without specifying why.
• In 2012, Sen. Jon Kyl said “impeachment is always a possibility”over Obama’s immigration policies.
• Last May, Rep. Jason Chaffetz said he was not pushing for impeachment, but didn’t rule out that Obama could be kicked out of officeover the Benghazi affair.
• In 2013, Sen. Tom Coburn told the audienceat a town-hall meeting that Obama was getting “perilously close” to qualifying for impeachment. Coburn’s fellow Oklahoma senator, James Inhofe, agreed.
• In 2013,  Kerry Bentivolio saidhis legislative dream would be to impeach Obama.
• During the debt-ceiling crisis, Rep. Louie Gohmert told an interviewerthat defaulting on the U.S. government’s debt would be an “impeachable offense.”
• While Sen. Ted Cruz has demurred on calls for Obama’s impeachment in the past, but has called it “a good question”and “a question for the House to assess.”

https://www.theatlantic.com/politics/archive/2014/06/a-brief-history-of-gop-calls-for-obamas-impeachment-from-benghazi-to-bergdahl/455544/

They reason they did not was because of the backlash from the Clinton impeachment  (The same reason Nancy Pelosi did not want to do so.) and no evidence of wrong doing.

Bill Clinton was investigated.  Because of Vince Foster and the Whitewater real estate investments of Bill Clinton.  A special investigation was created.  THE REPUBLICAN INVESTIGATOR found no evidence.  They brought Starr on board and there is evidence that Starr brought up irrelevant and unnecessary graphic and salacious allegations.

Bill Clinton was guilty of lying. The senate found him not guilty (and his approval rating spiked).

However, he submitted to the process. The senate called witnesses. Trump did not and the republicans did not allow a trial (a trial would have witnesses in my view).

Trump says he is being unfairly treated.  So does a teenager that peels out of the school parking lot and the cop watches the parking lot each day and pulls him over because he keeps driving recklessly.