Minnesota Democrat Keith Ellison has denied claims of domestic abuse days before his primary election for state attorney general.
His former girlfriend Karen Monahan and her son allege Mr Ellison once dragged her off a bed while screaming obscenities at her.
They claim there is also video footage of the incident, which Mr Ellison denied in a statement on Sunday.
He is a front-runner for the Democratic Minnesota attorney general candidacy.
"Karen and I were in a long-term relationship which ended in 2016, and I still care deeply for her well-being," Mr Ellison said in a statement on Sunday.
"This video does not exist because I have never behaved in this way, and any characterisation otherwise is false."
The Minnesota lawmaker is a top figure in the Democratic party. Last year, he became deputy chairman of the Democratic National Committee.
Ms Monahan shared her own statement with Fox 9 on Sunday, calling violence "an American tradition".
She said the alleged dragging incident occurred in 2016.
"I am a #METOO survivor," she wrote. "After several years of being in a relationship with Keith Ellison, it became clear, I had survived narcissist abuse."
She alleges that Mr Ellison threatened and intimidated her when she mentioned sharing her experiences with him in a memoir.
Ms Monahan also said she told Mr Ellison to seek help for his behaviours.
"I told him time and time again, I didn't want to share my story publicly, it was more important for healing and restoration to occur with this situation. I told him not only he deserved it, but his family and constituents deserve it as well.
"But no matter how many times I offered, he wouldn't take me up on it."
Ms Monahan's son Austin first posted on Facebook about the alleged incident on Saturday.
He claimed he found a video showing Mr Ellison dragging her off the bed and screaming at her to "get the [expletive] out of his house".
Mr Monahan also said he found text messages between Mr Ellison and Ms Monahan that showed "victim shaming", bullying and threats.
"I use[d] to believe the Democrats were the ones who would stand by a person who went through this kind of abuse," he wrote.
"Now I know both Democrats and Republicans could care less when it comes to violence toward women and girls."
Minnesota Public Radio (MPR) reported that after reviewing over 100 text and Twitter messages between Mr Ellison and Ms Monahan sent after their breakup, there was no evidence of the alleged physical abuse in those messages.
In one message, Ms Monahan said she wanted to write about the relationship, which Mr Ellison called "a horrible attack on my privacy", MPR reported.
Ms Monahan also sent MPR a screenshot of a 2017 message when she texted Mr Ellison: "We never discussed - the video I have of you trying to drag me off the bed."
Mr Ellison did not respond to her text, MPR reported.
His former wife, Kim Ellison, released a statement to US media saying: "We may be divorced, but we are still a family. I want members of our community to know that the behaviour described does not match the character of the Keith I know."
Mr Ellison has been a front-runner for the open attorney general's seat. Minnesota's primary election is on Tuesday.
Bernie Sanders endorsed Mr Ellison, and visited Minnesota to campaign for him earlier this year.
The six-term congressman is running against four other Democrats for the position.
Two opponents were quick to jump on the allegations.
State lawmaker Debra Hilstrom shared Mr Monahan's Facebook post on Saturday, saying "the incidents described are troubling".
This post was brought to my attention because I was tagged in this post. Domestic Violence is never ok. The incidents described are troubling. I call on Keith Ellison to answer these allegations.https://t.co/CQ1LSVfZqf— Debra Hilstrom (@debrahilstrom) August 12, 2018
Tom Foley, a former county attorney, has tweeted repeatedly about the allegations since Sunday.
He called for an "immediate investigation" and described Mr Ellison's denial as "Trumplike".
Explanation from @keithellison is #Trumplike denial. Here's why I'm calling for a criminal investigation into allegations of domestic abuse against Ellison by former girlfriend #DFL #MinnesotaAG #MinnesotaValues https://t.co/5JLkqUgUlQ— Tom Foley (@foleyforag) August 13, 2018
My message to @keithellison: You can try to run out the primary election clock but you can't hide. You need to answer these allegations now, for the sake of our voters and our democracy #DFL @StarTribune @PioneerPress @daveOrrick @Jessvanb @AmyHockert @kpottermn @andersoncooper https://t.co/2QYHav5EIg— Tom Foley (@foleyforag) August 12, 2018