Trump said he would give Warren a DNA test kit in the middle of a debate and offer $1 million for her favorite charity, "paid for by Trump, if you take the test and it shows you're an Indian". He has been sued for defamation by an adult film actress, Stormy Daniels, for calling her a liar for claiming she had an affair with Trump in 2006.
He tweeted about immigration after the rally as he flew to New Jersey, claiming that "a vote for Democrats in November is a vote to let MS-13 run wild in our communities, to let drugs pour into our cities, and to take jobs and benefits away from hardworking Americans".
No top Democrats in the U.S. House or Senate have called for such a move, though Democratic senators considered possible 2020 challengers to Trump, such as Kirsten Gillibrand and Kamala Harris, have floated the idea of scrapping the agency.
Warren was referring to the Health and Human Services Department's announcement that it will use DNA to confirm parent-child links as it tries to reunite families separated at the U.S. -Mexico borde.
Tester, who has been in office since 2007, has been complimentary of Trump on a number of issues in a state Trump handily won in 2016.
Trump also returned to themes of his presidency, stressing his hard-line immigration policies and support for law enforcement.
President Donald Trump is mocking journalists for questioning his readiness for his upcoming summit with Russian President Vladimir Putin. "I'll see what Trump has to say and how he delivers his magic words".
"I have a feeling she will say no", he added.
His barbs against the media came on a day when newsrooms across the US held a moment of silence in remembrance of five Maryland newspaper staffers who were fatally shot last week by a man who authorities say held a grudge against the publication.
Trump's revitalized attack of Warren was met with mixed applause, groans and cheers during an energetic campaign-style rally in Great Falls, Mont., on Thursday.
Trump's quip comes on the same day that the White House announced the hiring of former Fox News Channel executive Bill Shine, who was ousted from the network past year in the wake of lawsuits suggesting that he ignored alleged sexual harassment by Fox's late chairman and chief executive, Roger Ailes.
Jackson denied the allegations but ultimately withdrew his nomination.
Tester's ad sought to undermine Trump's efforts to boost Rosendale by pointing out that he and the president agree on several issues.
It may also be no coincidence that the #MeToo swipe came on the day the White House announced the appointment of Bill Shine, who traveled with Trump to Montana as deputy chief of staff for communications.
US intelligence agencies say Putin meddled in the 2016 election to benefit Trump.
The first and most important question - one Trump frequently raises during his travels - is whether he can defy historic omens and re-create robust turnout from his most loyal supporters that would mirror his stunning 2016 race and help lift Republican candidates. He blames Tester for derailing the nomination of White House physician Ronny Jackson as Veterans Affairs secretary. He went public with multiple allegations of misconduct against Jackson.
Tester planned to spend Thursday listening to farmers' and business owners' concerns about Trump's import tariffs and was expected to be driving back to his farm at the time of Trump's rally, spokeswoman Marnee Banks said.
"Welcome to Montana, and thank you President Trump for supporting Jon's legislation to help veterans and first responders, hold the VA accountable, and get rid of waste, fraud and abuse in the federal government", the ad read.
Rosendale, who is seeking to deny Tester a third term and give Montana an all-Republican congressional delegation, said Trump has focused on the race because of Tester's "liberal obstruction".