Democratic Sen. Jon Tester is now feeling the full weight of Washington Republicans’ drive to unseat him in the midterms, on the heels of President Trump's attacks for helping derail his pick to lead Veterans Affairs.

The National Republican Senatorial Committee plans to air a statewide ad for at least a week starting Wednesday, highlighting Trump's charge that the Montana senator's actions were a "disgrace."

GOP campaign arms also are spotlighting Tester's alleged support for so-called sanctuary cities and ties to his party’s liberal wing.

“Senator Tester has obstructed President Trump at every turn and now he’s paying the price,” Calvin Moore, a spokesman for the National Republican Senatorial Committee, told Fox News. “These developments really nuke his campaign strategy of trying to cozy up to President Trump, when all he’s really done has been to obstruct, obstruct, obstruct.”

He claimed the race has become "far more competitive."

The GOP candidates in the race don't have much national name recognition. And Republican strategists quietly admit that Tester’s reelection bid had until recent days “flown under the radar” -- even though he narrowly won his first two Senate races, and Trump defeated Democratic rival Hillary Clinton there by roughly 20 percentage points in 2016.

Tester, however, recently stepped into the spotlight in his role as top Democrat on the Senate committee that was reviewing White House physician Ronny Jackson's bid to become Veterans Affairs secretary.

Tester’s office made public a slew of allegations related to Jackson, a Navy admiral, allegedly over-prescribing drugs, drinking too much and more, though some of those allegations have been disputed.

Jackson, who called the allegations false, withdrew his nomination last Thursday. Within hours, Trump was calling on Tester to “resign” over his role, while suggesting he had damaging information on the senator.

“Allegations made by Senator Jon Tester against Admiral/Doctor Ron Jackson are proving false,” Trump tweeted. “The Secret Service is unable to confirm (in fact they deny) any of the phony Democrat charges which have absolutely devastated the wonderful Jackson family. Tester should resign. … Tester should lose race in Montana. Very dishonest and sick!”

Since then, Washington Republicans have been culling Tester’s voting records and trying to tie him to liberal Democratic Massachusetts Sen. Elizabeth Warren, who on Monday sent a fundraising email requesting money for Tester’s election and to fend off Trump’s attacks.

“Senator Jon Tester reminds me a lot of my big brothers back in Oklahoma (and it’s not just the flat top haircut),” she says in the email. “He’s not going to let himself get bullied by ANYONE. Not even the President of United States. … Will you make a donation to Jon Tester’s 2018 reelection campaign to help him in this fight.”

The NRSC’s Moore said in response: “Fresh off his false, partisan smear campaign of Rear Admiral Ronny Jackson, Senator Tester has now run to far-left icons like … Warren to rescue his failing campaign.”

The group also says Tester has voted three times since 2015 against withholding law-enforcement grants for cities with sanctuary laws, which effectively protect some illegal immigrants from deportation, and in February opposed $25 million for a U.S.-Mexico border wall.

“The migrant ‘caravan’ that is openly defying our border shows how weak & ineffective U.S. immigration laws are,” Trump tweeted Monday. “Yet Democrats like Jon Tester continue to support the open borders agenda – Tester even voted to protect Sanctuary Cities. We need lawmakers who will put America First.”

The Republican National Committee on Tuesday also released a batch of Tester voting records -- under the title “Two-Faced Tester” -- challenging Tester's claims of bipartisanship. The research shows Tester voted against the confirmation of 10 Cabinet-level nominees and Trump’s Supreme Court pick Neil Gorsuch.

The most recent Fox News' Power Rankings show the Montana race as a “toss-up.” Right now, Republicans have a 51-49 member Senate advantage.

There are 35 Senate seats up for election this year -- nine for Republicans and 26 for Democrats and independents who caucus with them. While Democrats are seen as having a shot at taking the House this year, Republicans have a built-in advantage in the Senate. Of the seven races Fox News rates as "toss-up," only one -- the race for retiring Arizona Sen. Jeff Flake's seat -- is held by a Republican.

Washington Republicans and some of their most deep-pocketed conservative support groups on Tuesday wouldn’t say whether they’ll now put more money or other resources into Montana.

But the state branch of Americans for Prosperity -- the conservative-libertarian advocacy group -- recently spent a reported $560,000 on TV and digital ads attacking Tester for supporting ObamaCare while allegedly failing to improve the health care law. Group officials did not respond to a question Tuesday about future plans.

Tester, meanwhile, has defended his actions during the VA secretary nomination process, saying the allegations were made by more than two dozen people who've worked with Jackson.

Tester campaign manager Christie Roberts dismissed the latest NRSC attack.

"This is just politics," she said. "Jon is relentless in holding government accountable and he will continue to fight for veterans to make sure they have the services they need and have earned."

Tester has also highlighted the concerns of Montana farmers about the administration's trade policies.

While Tester gets battered by national Republican outfits, unclear is whether any of the Republican contenders on the ground in Montana will be able to unseat him.

Three Republicans are competing to face Tester in the general election, with the primary just five weeks away.

They include better-known state Auditor Matt Rosendale, a former Montana legislator who lost a 2014 House race to now-Interior Secretary Ryan Zinke. But Troy Downing, a businessman, and Russell Fagg, a former state representative, are close behind, Republican media strategist Rory McShane said.

While the candidates may not be well-known outside Montana, McShane said they are serious candidates, each having raised roughly $1 million.

“Rosendale probably has the highest name recognition," he said. "But all of these guys are in the ball park. One million dollars is no joke in the Montana media market.”

Rosendale has endorsements from conservative GOP Sens. Ted Cruz, Texas; Mike Lee, Utah, and Rand Paul, Kentucky.

McShane predicted that one of the GOP candidates will now spend big on media in an attempt to pull away and that national Republicans and their donors will await the results and new polls -- then perhaps “jump in” before the general election really gets started.

The Associated Press contributed to this report.