(CNN) - Pressure is mounting for a small group of undecided senators from each party who have about two weeks to decide how they will vote on Supreme Court nominee Judge Brett Kavanaugh.
Several Democrats running for re-election in Republican stronghold states won by President Donald Trump are facing tough political choices ahead of the midterm election: Vote for Kavanaugh and upset their base Democratic voters, possibly dampening turnout in November, or vote against the judge and risk angering Trump supporters in their states who might otherwise vote for them.
For now, they aren't saying how they will vote, but it's notable that they haven't come out against him, as so many of their Democratic colleagues have done.
Asked Wednesday if she had seen any red flags about Kavanaugh, North Dakota Democratic Sen. Heidi Heitkamp said, "not that I've seen so far."
But she said she is still "reviewing his record."
Sen. Joe Donnelly, an Indiana Democrat up for re-election this year, also declined to say how he will vote.
"I'm still reviewing everything at this point," he said.
Another undecided Democrat, Sen. Jon Tester of Montana, said he wants to review the confirmation hearings transcript and meet in-person with Kavanaugh soon to "set the record straight" on some issues. Tester said he has concerns about Kavanaugh's record on abortion rights, security and campaign finance.
In the wake of Kavanaugh's contentious confirmation hearings last week, outside liberal groups including those who fear Kavanaugh's confirmation could lead to an overturning of Roe vs. Wade are ratcheting up pressure on Republican Sens. Lisa Murkowski of Alaska and Susan Collins of Maine -- both seen as potential swing votes in the nomination because they are pro-abortion rights -- with some attacks on Collins growing increasingly hostile, according to her staff.
In recent days, Collins's office has reported an increase in vulgar messages being directed at the senator and her staff. Several GOP senators blasted the liberal groups for targeting Collins.
"The increasingly aggressive behavior being employed by liberal activists and opponents of Judge Kavanaugh is extremely concerning. Targeting members in such a personal and hostile way has no place in public discourse, and Senator Schumer's continued silence sends a dangerous message to the Senate and country," Senate Majority Whip John Cornyn, the No. 2 Republican in the chamber, said in a statement. "It's time for Senator Schumer to make clear where he stands and disavow the mob rule of the radical Left."
Sen. Orrin Hatch of Utah, a member of the Judiciary Committee and the most senior Republican in the Senate, predicted the campaign against Collins wouldn't work and she would vote for the judge.
"She knows he's a class act and a reasonable guy," said Hatch who also said he expects Kavanaugh to be confirmed when a vote is expected during the last week of September.
A crowdfunding campaign has also threatened to fund a challenger against Collins if she votes for Kavanaugh.
"Bribery will not work on Senator Collins," said Annie Clark, a spokeswoman for Collins. "Extortion will not work on Senator Collins. And anybody who thinks these tactics would work on Senator Collins obviously doesn't know her. This crowdedfunded money to pressure her is based on a quid pro quo -- you vote the way we want and we will keep more than a million dollars away from your opponent -- vote against us and we give her the money. It is basically a bribe. Senator Collins will make up her mind based on the merits of the nomination. Threats or other attempts to bully her will not play a factor in her decision making whatsoever."
While Murkowski and Collins as well as three red state Democrats -- Heitkamp, Donnelly and Sen. Joe Manchin of West Virginia -- voted to advance Neil Gorsuch, Trump's first Supreme Court pick, the pressure from the liberal base has only intensified with Kavanaugh's nomination.
If all Republicans vote for Kavanaugh, they can clear him without Democrat support.
It's not clear when the closely-watched bipartisan groups of senators will announce their decisions. It's possible the Democrats, if any are going to support Kavanaugh, would hold off until after the Republicans announce they are backing him, so to avoid being tagged as the deciding vote in his favor and potentially angering liberal voters.