Montana, which elects both Republicans and Democrats to statewide office, strongly supported Trump in the 2016 presidential election, leading both Senate candidates to compete for Trump supporters.
"We'll take that little kit and say, we have to do it gently because we are in the Me Too generation, and we will very gently take that kit, slowly toss it" to her, Trump said, adding that he would offer $1 million to charity if she took the test and it "shows you are an Indian".
He also talked up his economic record, noting that USA unemployment hit an 18-year low in May, of 3.9 percent, and that the economy has added 3.4 million jobs since he became president 18 months ago. She has been calling for his impeachment for more than a year.
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. Trump also claims that Democrats "couldn't give a damn" about law enforcement.
Trump also commented on his upcoming trip to Europe where, among other stops, he will meet directly with Russian President Vladimir Putin. "And I said, 'You know, Angela, I can't guarantee it, but we're protecting you and it means a lot more to you than protecting us 'cause I don't know how much protection we get by protecting you".
His barbs against the media came on a day when newsrooms across the USA 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.
President Donald Trump described a hypothetical re-election contest against Senator Elizabeth Warren at a rally on Thursday and said the Massachusetts Democrat should be tested "very gently" for Native American heritage.
The support for Cruz belies Rosendale's attempt to tie himself to Trump, but seemingly did not - because of Trump's visit - run afoul of a loyalty test the White House is running when deciding endorsements in the midterms.
Trump singled out Tester in April, saying the farmer "will have a big price to pay" for releasing allegations against Jackson that included on-the-job drunkenness, overprescribing medication and fostering a hostile work environment.
Jackson denied the allegations but ultimately withdrew his nomination.
Trump's rally on Thursday was a classic display of virtuoso demagoguery and hardball populism that has already been aimed at red-state Democrats like Sens.
Two days before Rosendale's name was included on the list, Cruz told conservative radio host Mark Levin that Trump is "a NY liberal who is pretending to be a conservative to try to fool Republican primary voters".
Security for the event has prevented any mad scrambles for the best seats in the house, but the arena is expected to be packed when President Trump arrives.
Trump planned to rally supporters Thursday in Great Falls in a bid to boost the candidacy of state Auditor Matt Rosendale, the Republican challenger to Tester. The president has made the Montana race a priority as he hopes to help Republicans tighten the party's hold on the Senate. He blames Tester for derailing the nomination of White House physician Ronny Jackson as Veterans Affairs secretary.
Tester tried to counter that narrative before Trump got to the state by taking out a full-page ad in more than a dozen newspapers across the state thanking him for signing 16 bills the Democrat sponsored or co-sponsored.
Trump mused that he would buy a DNA test and throw it at her should he face off with the MA lawmaker during a 2020 presidential debate - and she brings up the claim.
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". While Tester opposed Trump's first Supreme Court nominee, Neil Gorsuch, and the Republican tax bill, he has also taken flak from the left for a bill easing the rules on banks.