McConnell, 77, won his last re-election bid - in 2014 - with 56 per cent of the vote and Donald Trump carried Kentucky with 63 percent in the last presidential election. Chuck Schumer of NY, who has had difficulty persuading top-tier candidates in other states to take on incumbent Republicans with control of the Senate at stake.
Massachusetts' Elizabeth Warren said in a tweet that McGrath "is a real fighter for working families in Kentucky", adding, "Go Amy!" "Well, that started with this man, who was elected a lifetime ago", McGrath says of McConnell.
"I felt like somebody needs to stand up to him", McGrath said.
McConnell's campaign wasted no time picking up on that theme, unveiling a website called wrongpathmcgrath.com with a video features McGrath quotes about abortion and health insurance and composite images showing McGrath alongside such liberal leaders such as Sen. "I'm Amy McGrath, and I've often wondered, how many other people did Mitch McConnell never take the time to write back or even think about?"
The Senate majority leader's tone was more sanguine.
She retired from the Marines in 2017 and moved back to Kentucky, before she ran a strong campaign against Andy Barr in the state's 6th Congressional District, even though she lost.
Since becoming party leader, McConnell said he notices he gets "more attention than I used to".
Amy McGrath address supporters after her loss during her Election Night Event at the EKU Center for the Arts on November 6, 2018, in Richmond, Ky.
Democrats' thoughts on reparations have changed since then, with numerous 2020 presidential candidates coming out in support of some kind of reparation system for descendants of slaves.
McGrath will have to win the Democratic nomination to have the opportunity to face McConnell.
McConnell's website also indicates he would try to make one of McGrath's potential strengths a liability.
In that race, McGrath, a Naval Academy graduate, foreswore negative attack ads against Barr while he and several outside groups supporting him spent millions of dollars labeling her as "too liberal" for Kentucky.
'He has been around for 34 years and I think this is different.
McConnell has in Kentucky a fiercely loyal team of political operatives who are known for hard-hitting campaigns that leave his opponents badly bruised.
Democrats, still sore that McConnell blocked a Senate hearing for President Obama's 2016 Supreme Court nominee, Merrick Garland, see the seat as a top target in 2020.