By Lesley Clark

McClatchy Washington Bureau

WASHINGTON, D.C. — Worried about the Republican Senate’s inability to deliver on big campaign promises, the White House and its allies are making a strong push to get at least three vulnerable Senate Democrats to back the administration’s tax reform agenda.

The shaky Democrats, all up for re-election next year in states that President Donald Trump won handily, have already signaled interest in working across the aisle — even as their Democratic colleagues have urged unity in fighting any GOP tax plan that disproportionately helps the rich.

“We are confident right now that we will be able to earn (Democrats’) support with our tax reform agenda,” said Marc Short, the White House director of legislative affairs. Administration officials, he said, have had discussions with vulnerable Senate and House Democrats.

Republicans were particularly cheered when Democratic Sens. Joe Donnelly of Indiana, Heidi Heitkamp of North Dakota and Joe Manchin of West Virginia declined to sign a Senate Democratic caucus letter to Trump and congressional leaders detailing what is not acceptable in a tax plan, notably a tax cut for the top 1 percent of Americans. Every other Democrat and the two senators who caucus with them signed the letter.

Instead, Manchin said in a statement that he’s “particularly excited” to work on tax reform with Trump, who crushed Democratic presidential rival Hillary Clinton in West Virginia, winning 68 percent of the vote.

Trump drew thousands to a rally in Huntington Thursday night, celebrating the decision Thursday by West Virginia’s Democratic governor, Jim Justice, to change party affiliation and become a Republican.

In Washington, Manchin dismissed the Democratic tax letter as a stunt.

“Press releases don’t solve problems, people do,” he said. “Now is not the time to make tax reform harder. Now is the time to get everyone involved and put everything on the table.”

Heitkamp is up for re-election in a state Trump won by 36 percentage points. She declined to sign the letter, saying “We shouldn’t prejudge any of this.” Donnelly represents Indiana, where Trump won by 19.

In addition to the White House, the political network associated with the billionaire brothers Charles Koch and David Koch has is trying to prod the vulnerable Democrats to join the Republicans.

“With the opportunity to unrig the American economy now in front of him, Manchin shouldn’t let this chance at meaningful tax reform pass by,” Freedom Partners, part of the Koch network, said in an email showcasing Manchin’s past remarks in favor of tax reform.

The pitch to Senate Democrats comes as Republicans have struggled to reach consensus within their own ranks and give Trump a big legislative victory. A years-long pledge to repeal the Affordable Care Act collapsed in the Senate last month when three Republicans rejected the GOP leadership’s initiative.

Although Senate Majority Leader Mitch McConnell, R-Ky., has said he’ll try to use a procedural maneuver to allow debate on the tax overhaul to be cut off with 51 votes instead of the traditional 60, Republicans hold a narrow margin of just 52 seats in the chamber. That means Democrats could cast deciding votes.

The White House has “learned how difficult it is to thread the needle with 52 senators,” Short said.

The administration has already had conversations with more than 200 members of Congress, including members of the House’s Blue Dog Coalition of fiscally conservative Democrats and the Problem Solvers Caucus, a group of Republicans and Democrats. The administration has also spoken with red state Senate Democrats, Short said.

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Democrats next year will defend the seats of 25 senators who caucus with them. Among them are incumbents from 10 states that Trump won in November.

It’s important for the three targeted Democrats to show independence, said David Heller, a Democratic campaign strategist whose clients include Donnelly and other red-state Democrats.

“They’re eager to show voters that they will work with Democrats and Republicans to do whatever is best for their state,” he said. “They’re willing to buck the party line on issues like this.”

Democrats displayed uncommon unity in fighting Republican efforts to repeal and replace Obamacare, but tax reform is “not something that Democrats would go to the mats on like they did on health care,” Heller said. “If Joe Manchin and the other Democrats can say ‘I reduced taxes and protected your health care,’ that’s a winning message.”

Manchin is facing a primary challenge from Paula Jean Swearengin, an activist backed by Brand New Congress, a group launched by former staffers of Bernie Sanders’ presidential campaign.

David Donnelly, president and CEO of the money-in-politics watchdog group, Every Voice, warned that Democrats who vote for a tax cut that solely benefits the rich could find themselves in trouble with middle class voters.

“They may have the strategic need to say ‘I’m listening,’ but even in red states, giving tax cuts to millionaires and billionaires is not necessarily the strongest position to be in,” said Donnelly. His group says the involvement of the Koch network “is a sign the administration is prioritizing passing policies to benefit wealthy donors.”

Manchin, who won reelection in 2012 with 60.6 percent of the vote, already has Republican challengers: Rep. Evan Jenkins, R-W.Va., state Attorney General Patrick Morrisey.