On The Rachel Maddow Show Friday, Rachel explained why Tuesday's recall vote in Wisconsin is crucial— she called it the second-most important election this year— how the unions are at stake in Wisconsin, and how they're a key source of Democratic strength.

Maddow:

Excerpt from the Rachel Maddow Show

Here’s the most important thing we have learned since Wisconsin’s [union-stripping] law went into effect: it has served the purpose Governor Walker intended for it: It has killed the unions in Wisconsin. 

This chart shows union membership nationwide, from the 1950s to the present. The decline you see has been driven by one thing—by corporations getting their way, and getting non-union workforces in the private sector.

But even with this precipitous decline in union membership, still nearly one in eight American workers belongs to a union. Public-sector unions have held on. They’ve remained stable even as membership in private unions has plummeted.

That public-sector unions remain relatively strong has implications for Americans who work as teachers and bus drivers and so on. It makes a difference in whether those working people are working for a living wage. And that supports all working-class wages.

The strength of public-sector unions has also blunt political implications.

These were the heavyweights when it came to outside spending in the 2010 election cycle. These were the 10 groups that spent the most money on that election that year. Six of the 10 groups spent big-time on the right. And they were led by the corporate-funded U.S. Chamber of Commerce, far and away the biggest spender that year.  Almost all the groups spending on behalf of Republicans in 2010 were corporate-funded groups.

The only major spenders on behalf of Democrats that year were unions, that was it. And they only made up 3 of the top 10 spenders.

If you kill public sector unions in Wisconsin, you can kill unions all together, and you can kill this key source of Democratic strength.

And in Wisconsin, that’s exactly what Republicans have done.

Because they could not stop the implementing of this law, the Democratic side in the Wisconsin recall fight does not have the means to compete that they usually have. That’s a major reason for why the Republican side have had a spending advantage in this campaign that at times has reached 25 to 1...

The election, even so, is really close.

Democrats might yet pull it off. But killing off the unions is what Republicans want to do in every state in the country. That’s why Scott Walker is their poster boy. Republicans understand that this is the way they can win not just now, but forever.

Watch the full segment here. Plus, video from the Maddow show on how the four Wisconsin state senate race recalls are also critical.