The protest began at 12:30 p.m. on Thursday at the Barrett Prettyman Courthouse - where Kavanaugh now sits as a judge - and will culminate at the Supreme Court.
In the op-ed, Kavanaugh stood firm in his assertion that, if confirmed, he'd be a trusted associate justice, writing that the US could count on him "to be the same kind of judge and person I have been for my entire 28-year legal career: hardworking, even-keeled, open-minded, independent and dedicated to the Constitution and the public good".
Another undecided Democrat, Joe Manchin of West Virginia, remained undecided on Thursday afternoon.
Senators received the 46-page report Thursday after it was delivered to the White House at 2:30 a.m.
Committee chairman Chuck Grassley issued a statement around midnight that listed the 10 people interviewed by the Federal Bureau of Investigation, although not all of them were named.
Mr Trump said the protesters and "their rage-fuelled resistance is starting to backfire at a level nobody has ever seen before".
Another undecided Republican, Lisa Murkowski of Alaska, was asked whether Trump's comments would affect her decision on whether to back Kavanaugh's confirmation.
Kavanaugh called the judicial system the "crown jewel of our constitutional republic" and noted that the Supreme Court is "the last line of defense for the separation of powers, and for the rights and liberties guaranteed by the Constitution". This arrives hours before The Senate will vote for his confirmation on Friday morning, and reach a final vote on October 6.
The protesters include a loud contingent from ME, and they're calling on Susan Collins, a key Republican senator, to vote against Kavanaugh.
With a razor-thin majority in the upper chamber, Senate Republicans can afford to lose only one GOP vote if all Democrats vote against the nomination. Sen.
Earlier this week Donald Trump was criticised for imitating Dr Ford at a rally in Mississippi.
Kavanaugh and California professor Christine Blasey Ford testified in front of the committee on September 27.
Demonstrators wait in-line to enter Hart Senate Office Building for a protest against the confirmation of Supreme Court nominee Judge Brett Kavanaugh. Republicans did not want to pursue whether Kavanaugh lied to the Senate Judiciary Committee about his alcohol use in high school and college.
Republicans expressed growing confidence that Kavanaugh would be confirmed by the Senate after a political battle that has riveted Americans weeks before November 6 elections in which Democrats are trying to take control of Congress from the Republicans. Just a single copy of the report was produced, and that was not made public.
Ford, who testified last week at a dramatic Judiciary Committee hearing, accused Kavanaugh of pinning her down, trying to remove his clothing and covering her mouth when she screamed.
"When the noise fades, when the uncorroborated mud washes away, what's left is the distinguished nominee who stands before us", Senate Majority Leader Mitch McConnell said on the Senate floor.