Senate Democrats' letter to Trump on tax reform is missing something that could be the key to a GOP success

Senate Democrats released a letter on Tuesday with a list of baseline demands to come to the table and negotiate on a tax reform bill with Republicans.

While the letter contained a list of items that could earn their support on tax reform legislation, perhaps more notable was what was missing.

Three Democratic senators did not sign onto the letter: Joe Manchin of West Virginia, Heidi Heitkamp of North Dakota, and Joe Donnelly of Indiana.

All three face reelection bids in 2018 in states President Donald Trump won by huge margins last year.

Currently, the tax reform effort is still in its infant stages. The Trump administration released a one-page outline of "principles" in April, while key administration officials and GOP congressional leadership released a letter on July 27 asserting their shared principles for a bill.

According to reports, the White House is aiming to get tax reform done by the end of 2017. The GOP plans to debut tax reform legislation in September, get it through the House in October and the Senate in November, and proceed through a conference to get the bill to Trump's desk by December.

Given that there could be some dissent from Republicans on various aspects of the plan - whether it is revenue neutral, the lack of a border-adjustment tax, or deductions that favor certain states - winning over some vulnerable Democrats could be important to getting any tax bill through Congress.

When asked the non-signature, a spokesperson for Donnelly simply said that the Indiana senator wants tax reform to be done in a bipartisan fashion.

"Donnelly believes there should be a bipartisan process to reform our tax code," the spokesperson said in an email. "He believes our tax code should be reformed in a way that gives working and middle-class families greater economic security, rewards companies that invest in American workers as outlined in his End Outsourcing Act, and is revenue-neutral. He is ready to exchange ideas with others in Congress and the Trump Administration."

Spokespeople for Heitkamp and Manchin did not respond to requests for comment.

Manchin is particularly vulnerable, given that Trump won his state by 41.7 percentage points in 2016. The West Virginia senator also bucked his party previously by voting for the confirmation of Attorney General Jeff Sessions, being the only Democrat to do so.

Additionally, the Manchin-Donnelly-Heitkamp trio were the only Democrats to vote for the confirmation of Supreme Court Justice Neil Gorsuch.