A pro-impeachment group is targeting GOP senators in battleground states with a round of ads as they try to build pressure on Republicans to break with President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE in the growing battle.

Need to Impeach, which is mainly funded by Democratic presidential candidate Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE, announced that it would run $3.1 million in TV and digital ads against Republicans in a number of key races.

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The group will target Sens. Martha McSally Martha Elizabeth McSallyOn The Trail: Making sense of this week's polling tsunami The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ariz.), Cory Gardner Cory Scott GardnerBreaking the Chinese space addiction Trump dumbfounds GOP with latest unforced error Billionaire who donated to Trump in 2016 donates to Biden MORE (R-Colo.), Joni Ernst Joni Kay ErnstOn The Trail: Making sense of this week's polling tsunami Tillis appears to reinforce question about COVID-19 death toll The power of incumbency: How Trump is using the Oval Office to win reelection MORE (R-Iowa) and Susan Collins Susan Margaret CollinsDemocratic senator to party: 'A little message discipline wouldn't kill us' Poll: 57 percent of Americans think next president, Senate should fill Ginsburg vacancy On The Trail: Making sense of this week's polling tsunami MORE (R-Maine) over the next two weeks, while lawmakers are back in their home states for the recess.

"More and more voters are realizing in this moment that politicians cannot represent Americans if they don’t represent American values. And there’s no job more important for U.S. Senators than standing up for the constitution,” Nathaly Arriola, the executive director of Need to Impeach, said in a statement.

More than half of the group's ad buy will go toward TV ads, which are expected to start airing Thursday. The rest will go to digital ads, which are starting immediately.

The push to target Senate Republicans comes after the House launched a formal impeachment inquiry last week, raising the chances that impeachment articles could be sent to the Senate.

No Republican senator has said they would support impeachment, or even that they support on impeachment inquiry.

A CNBC All-America Economic Survey released on Monday found that 47 percent of respondents oppose impeachment, compared with 44 percent who approve.

But 88 percent of surveyed Republicans, according to the same poll, oppose impeaching Trump.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellDemocratic senator to party: 'A little message discipline wouldn't kill us' House to vote on resolution affirming peaceful transition of power Republican lawyers brush off Trump's election comments MORE (R-Ky.) said earlier this week that he would have "no choice" but to take up impeachment if the House sends over articles.

"Well under the Senate rules we're required to take it up if the House does go down that path and we'll follow the Senate rules," McConnell said during an interview with CNBC.