Robby Mook and Jeff Weaver say in the memo that the tax effort is "already resoundingly unpopular across just about every demographic," including the rural and suburban voters who flocked to Trump last year and the Democratic base voters who sat out the election.
That has given Democrats a way to avoid having to decide which of those groups to pour money and organizing efforts into winning back in the 2018 midterm elections, they write.
"It is quite a feat for Republicans to have designed a bill that could alienate Obama-Trump voters, Romney-Clinton voters and base Democrats all at the same time, but the tax plan achieves exactly this trifecta," Mook and Weaver write in the memo.
"Should the legislation reach President Trump's desk, the issue has the potential to doom Republican lawmakers who vote for it. If Democrats properly seize this issue, they can potentially win over most every swath of the electorate critical to next year's midterm elections."
The memo comes with Senate Republicans poised to approve their tax bill on a narrow, party-line vote.
Congressional Republicans have cast the bill's passage as crucial to delivering a tangible legislative victory to the base that handed them the House, Senate and White House in last year's elections.
But Democrats -- including Mook, now a CNN political commentator, and Weaver, who became something of a political odd couple near the end of the party's combative primary last year -- see in it an opportunity to make an economic argument that could help heal the rifts over which voters the party most needs to court, at the expense of others, that have lingered since Clinton's loss to Trump.
Mook and Weaver argue in their memo that the bill helps corporations and wealthy Americans and includes protections for special interests that are anathema to voters who bought into Trump's "anti-'swamp' rhetoric."
They point to the GOP's move to ditch the state and local tax deduction as one that will hike taxes on suburban households in states like New York, California, New Jersey and Pennsylvania -- all of which have competitive House races in 2018.
The proposed repeal of the Affordable Care Act's individual coverage mandate, which is included in the Senate bill
, is likely to increase insurance premiums, they say.
"The Republican tax plan is the rare piece of legislation that manages to provide something for nearly everyone to hate," Mook and Weaver say in the memo.
The tax bill becomes more unpopular as voters are exposed to messages about what it would do, the memo says, citing polling from the Democratic super PAC Priorities USA.
"The tax proposal is the best opportunity yet for Democrats to convince voters that Donald Trump and congressional Republicans are looking out for their wealthy donors, and not working-class Americans," Mook and Weaver write.
"The widespread opposition to the Republicans' plan should reassure Democrats that they ought not engage in some false choice between different groups of voter targets," they write. "Our party should compete everywhere, and seek to win over voters of all ages, education backgrounds and income levels by using the tax fight to illustrate the two parties' vastly different priorities. If Democrats seize this opportunity, congressional Republicans who support the tax plan will definitely be doing so at their own political peril."