Washington(CNN) Three Democrats from states President Donald Trump won in 2016 will join the President on Tuesday evening for dinner as the White House seeks support for sweeping tax reform, congressional aides said.

Multiple sources said the White House legislative operation viewed North Dakota Sen. Heidi Heitkamp, Indiana Sen. Joe Donnelly and West Virginia Joe Manchin -- all moderate Democrats facing re-election in 2018 -- as "gettable" Democrats on an otherwise partisan legislative push to slash taxes for corporations and overhaul the system.

Three Republican senators were also due to attend the dinner Tuesday: Sen. Pat Toomey of Pennsylvania, Sen. Orrin Hatch of Utah and Sen. John Thune of South Dakota.

Two White House officials go to Capitol Hill

The dinner comes as Trump's tax reform point men -- Treasury Secretary Steven Mnuchin and National Economic Council Director Gary Cohn -- headed to Capitol Hill to solidify the effort. The two had a Hill meeting on Tuesday as part of the so-called "Big Six," a group that also includes four top GOP negotiators on Capitol Hill. Separately, two sources said Mnuchin and Cohn would meet with Republican members of the Senate budget committee. The latter meeting's purpose would be to try kick starting an effort to coalesce around the budget proposal for the coming fiscal year.

Director of the National Economic Council Gary Cohn and Treasury Secretary Steve Mnuchin look on as US President Donald Trump delivers remarks following a meeting on infrastructure at Trump Tower, August 15, 2017 in New York City.

Mnuchin and Cohn declined to comment as they walked out of the "Bix Six" meeting.

Hatch, the Senate finance committee chairman and a member of the tax group, told reporters "we'll have to see" if the House and Senate would release one tax plan together or one for each chamber.

"We're trying to put it together so both the House and the Senate can work together on it," Hatch said. "Hopefully we can work it out."

Asked if it was necessary to give conservatives more details on what leadership is working on in order to assuage their concerns, Hatch demurred, saying, "That's up to the leadership."

Hatch announced later Tuesday afternoon he planned to convene a hearing next Tuesday on ways changes to the tax code could improve the situation for business.

Establishing a budget proposal would overcome a key hurdle for tax reform, which Republicans must find a way to pay for in order to pass through the Senate with a simple majority vote. Under the rules of the Senate, Republicans can pass tax reform with a simple majority vote only if the plan would not increase the nation's deficit outside of the 10-year budget window.

The top negotiators -- who along with Cohn and Mnuchin include House Speaker Paul Ryan, Senate Majority Leader Mitch McConnell, Hatch and House Ways and Means Committee Chairman Kevin Brady -- have been hammering through the details and disputes of the forthcoming proposal for months. Those meetings have ticked up in frequency and have started to branch out to include outreach to the members of the key tax writing committees as leaders attempt to get their members comfortable with the coming effort.

Brady is scheduled to brief the House GOP conference Wednesday on the status of the negotiations. It is a crucial component of the process, aides say, with leaders cognizant of the perception that members were left out of the process of drafting the Republican plan to repeal and replace Obamacare, dooming it to eventual failure.

Still, aides in both chambers acknowledge the path forward is more difficult than not given the constant tug of special interests, state and district priorities and ideological baselines.

'We want to sit down with anybody'

White House press secretary Sarah Sanders said at the press briefing Tuesday afternoon that guests for the White House dinner were chosen "by their willingness to want to sit down and have these conversations with the President."

Asked about the potential for including Montana Sen. Jon Tester, another red state Democrat up for re-eleciton in 2018, in tax talks, Sanders said, "We want to sit down with anybody who is willing to be serious about real tax reform for this country, about providing real relief for middle class America, and actually looking to make bold changes."

"Those are the conversations we want to have," Sanders said. "And I would imagine if Senator Tester wants to be involved in those and is serious about it, we'd certainly be willing to have that conversation with him."

Mnuchin acknowledged the difficulty of passing the massive tax cuts Trump called for without ballooning the deficit. He said at an event hosted by CNBC that they might not be able to get the corporate tax rate down to 15% "given the budget issues." But even with an increasingly stacked legislative calendar going into the end of the year, Mnuchin maintained his position that the Republicans would pass tax reform by the end of the year.

Mnuchin's outreach to the Senate on Tuesday would come after his muddled attempt last week to mollify outraged House conservatives over a deal Trump brokered with Democratic leaders to tie three-month extensions of government spending and the debt ceiling to hurricane relief funds.

Trump delivered a speech in Heitkamp's homestate of North Dakota earlier in September, bringing the Democratic senator along with him on Air Force One and calling her a "good woman." Aides say future visits in states that are home to Democratic senators where Trump won handily in 2016 will come in the weeks ahead.