President Donald Trump uttered the "S"word — shutdown — on Tuesday, and it could be the best news ever for his domestic agenda.

The political class and the usual suspect pundits have turned shutdowns and the threat of shutdowns into some form of mythical political suicide. But a shutdown is likely the only way for the Trump team to shake the leaders of both parties in Congress out of their perpetual spending frenzy. It's worked before and it very well could work again. All we needed was someone to have the courage to carry out at least a shutdown threat and trigger one if necessary.

President Trump outlined the reasons why he might need a shutdown in a few tweets when he referenced the sub-60 vote reality in the Senate for the Republican Party. Knowing this, the Democrats in the Senate and the House have a real incentive to demand no cuts to the spending agenda and regime they crafted during the Obama years. And with the stopgap spending bill the Congressional Republicans just sheepishly agreed to this past weekend as proof, we know the GOP simply caved to those Democrat demands.

So, why didn't the Republicans use a possible shutdown to stand up to the Democrats and cut the spending? The reason is fear. Republicans are afraid because the conventional wisdom says that shutdowns are incredibly toxic with the voters and whichever leader or party gets the blame for any given shutdown is toast at the ballot box.

The conventional wisdom is wrong.

Because history tells a different story. With very few exceptions, voters have simply not moved to punish anyone for any shutdowns in the modern era. The latest example was the government shutdown over Obamacare in late 2013. Poll after poll showed the public blamed the Republicans for that shutdown and most experts predicted severe electoral doom for the GOP even though they eventually caved in that shutdown battle. But that doom never happened. A year later not only did the Republicans retain the House, but they finally regained control of the Senate in a massive midterm election landslide. And the biggest reason for that win was voter anger over — you guessed it — Obamacare.

Look back a little further and you see similar lessons. The government shutdown engineered by the Republicans in 1995 not only helped bring about important legislative compromises with the Clinton administration in the months that followed, but it also did not result in the GOP losing control of Congress a year later. President Clinton even got re-elected too. For the GOP, Bill Clinton, and the country, that was a win/win/win.

And when the Democratic Party-controlled House and President Ronald Reagan locked horns and caused a total of seven government shutdowns from 1981 to 1986, neither Congressional Democrats nor Reagan lost their control of the House or the White House in the subsequent elections, respectively.

Time after time, the voters have reacted to shutdowns the same way. Sure, they may respond angrily to pollsters while the shutdowns are in effect. But the long-term voting results are almost an empty set. It's the political equivalent of a referee just "letting the guys play."

But the Republicans have not learned this lesson. Even after their big 2014 win,the Republican leadership of Senate Majority Leader Mitch McConnell and then-House Speaker John Boehner not only didn't trigger another shutdown to further stop Obamacare or the impending Iranian nuclear deal, they pre-emptively promised not to even threaten to do so. By surrendering the congressional"power of the purse" before they even officially retook control of both houses of Congress, many Tea Party and other conservative Republican voters lost faith in the party establishment. And that likely played a big role in the defeat of all the GOP establishment candidates for president in the 2016 primaries.

This is all the long way of explaining that, by threatening a shutdown, President Trump is simultaneously reconnecting with his voter base, goosing the cowardly Republican leadership, and brandishing his best bargaining weapon against the Congressional Democrats. And while the White House can be excused for waiting a mere 100 days or so to do this, the Republican leaders on Capitol Hill cannot after sitting on their Constitutional budgeting duty for more than 2 years.

Again,the assembled wise men and women of Washington are already sounding alarm bells over Trump's shutdown cheerleading. That's entirely predictable. But either they're ignorant of history or deliberately suppressing the fact that shutdowns are actually a relatively low-risk exercise in political courage.

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

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