Senate Majority Leader Mitch McConnell has voted in support of President Trump's positions during the 116th session of Congress on all issues related to border security and funding, immigration reform, tariffs, budget bills, nominations and all foreign policy with the exception of withdrawal of US forces in Afghanistan and Syria. During the 115th congress, Senator McConnell voted in line with President Trump on all major measures with the exception of sanctions of Russia, Iran and North Korea, and a four week funding extension.
As the Majority Leader Mitch is frequently in the news which almost always portrays him negatively. He has been a politician for a long time and for that reason alone some Republicans do not support him. Many polls such as Morning Consult, RCP and The Atlantic say that he is unpopular - but the accuracy of these polls is questionable.
Senator McConnell will likely receive an endorsement from President Trump, who has invested tremendous effort into their working relationship. Mitch will also most likely win reelection in 2020. Mitch has won all 9 of his last elections and has over $8 million as of 09/30/19.