The Normaton, Pontefract and Castleford representative spoke out after Joshua Spencer from Knottingley was jailed today for nine weeks.The 25-year-old sent a message to a friend calling the MP a "whore" and said he was going to pay a drug addict £100 to attack her.
Ms Cooper said: "There has been something very sad as well as very grim about dealing with this.
"Even just a few years ago I would never have imagined being involved in a court case where a local candidate or officer in another political party had made threats of violence.
"Politics needs to be better than this. All of us in politics from the Prime Minister and party leaders to MPs, candidates and local activists in all political parties have a responsibility to make it so.
"Disagreement and debate are a healthy part of our politics. But violent or inflammatory threats, attempts at intimidation, abuse or aggression, online and offline, undermine our democracy. All of us have a responsibility to make sure it never becomes normal, accepted or seeps into election campaigning.
“As MPs we have a job to do, helping all our constituents, standing firm against any kind of intimidation or threat and also trying to show everyone kindness and respect. I won’t ever stop doing that. And I hope this is a chance for people across politics and across our communities to come together and show we won’t ever accept these kinds of threats towards others we disagree with.
“I have asked the Conservative Party what action they took last year after the investigation began, why Mr Spencer was still able to attend the General Election count as their representative after he had been summonsed, whether anyone locally or nationally in the party had raised concerns about his behaviour or position and what action they are taking now.
"But I urge all political parties and campaigners across the country to reaffirm their commitment to a better, kinder politics than this.”