"Jumping on board at least as willing negotiating partners gives Democrats a major policy goal achievement, a link to patronage programs for decades to come, and a chance to weaken a Congressional GOP already badly bruised by the Obamacare replacement bill in-fighting."

The other reason why the Democrats need to reconsider their position can be summed up in two words: "missed opportunities."

Sure, the initial funding for the big Trump infrastructure plan is designed to come from and be managed mostly by the private sector. As a lifelong developer, Trump isn't likely to brush that part of the plan completely aside.

If the Democrats come to the negotiating table however, demanding more significant government spending and management of the plan, they'll have some legs to stand on. Back during the election and the transition process, both President Trump and top adviser Steve Bannon noted how historically rock bottom interest rates make now the best time to do more government borrowing. In that way, this administration isn't as likely to stick to ideological fiscal guns on this one.

And another great thing about infrastructure projects from the liberal/Keynesian perspective is that once they're built, the story isn't over. Roads, bridges, airports, and power grids need perpetual maintenance and upgrades, and that means the government will always have a role to play in at least choosing which private companies get the contracts to do that work.

Finally, there's the opportunity the Democrats would be missing to drive a further wedge between the anti-deficit spending Freedom Caucus types in the GOP and the majority of the congressional Republicans who won't be able to resist either supporting President Trump or getting their own hands on some of that $1 trillion for their own districts. That's because no matter how much the private sector funds and engineers the Trump plan, some conservatives in Congress are not loving yet another big spending plan.

So let's sum up: Jumping on board at least as willing negotiating partners as the Trump infrastructure plan is crafted gives the Democrats a major policy goal achievement, a link to patronage programs for decades to come, and a chance to weaken a Congressional GOP already badly bruised by the Obamacare replacement bill in-fighting.

Why would the Democrats walk away from this opportunity? The only legitimate reason would be that they found absolutely no compromise offers from the White House or the Republican Congressional leaders on paring some of the private sector role in the plan.

A less legitimate one would be a singular obsession with destroying the Trump presidency at all costs. Certainly the left-wing of the party would prefer the Democrats focus on Russiagate and stop the president at every turn.

The Democrats would be wiser to avoid the appearance of working only to undermine Trump at the expense of voters' priorities, starting with jobs. If they block this plan without going to the negotiating table, they run the risk of the American voters blaming them every time they hit a pothole on the road or suffer from flight delays. That's a big gamble.

A better strategy would be to follow the GOP Congressional example from the mid-1990s when House Speaker Newt Gingrich proved the Republicans weren't just about the Whitewater investigation and he struck major tax and welfare deals with the Clinton White House. That deal helped the GOP keep control of Congress for another decade and kept the Republicans relevant enough to take back the White House in 2000.

It's still early enough in that $1 trillion infrastructure party for the Democrats to make a crucial appearance. They don't have to eat all the food, drink all the wine, or even play all the party games. But they need to be there.

Otherwise they risk further hurting their image as a pro-jobs party for decades and holding the nation's roads and airports hostage in the process. Even in Washington, $1 trillion is a lot of money. It should be enough to turn this Democratic partisan warfare aside.

Commentary by Jake Novak, CNBC.com senior columnist. Follow him on Twitter @jakejakeny.

For more insight from CNBC contributors, follow @CNBCopinion on Twitter.