a doubling down in militarized police departments?

Should "in" be "on" in "a doubling down in militarized police departments"?
And it means "the bet on MPD will be doubled"?

Source (from an online post today):

I can't speak for anyone else, but I'm not motivated out of some dimwitted need to bend others to my will and "scare" or "bully" them into voting for Hillary. I think the most accurate description of the nature of my motivation would be abject fear of the obvious destruction that we'd invite by putting Trump or Cruz in the White House. I don't expect anyone else to look at Cruz and Trump and see the absolute monsters I do, but I would ask people to believe me when I say that's what I see. When I look at Cruz and Trump I see at least one, and maybe more senseless wars laying waste to thousands of American lives and billions in dollars. I see an immediate all out effort to roll back gains in healthcare, women's reproductive rights, the right to marry and income inequality, I see a doubling down in militarized police departments and an attempt to further weaken existing gun control. With a Trump or Cruz as president, I see a country given tacit permission to be more hateful, and less tolerant to everyone who isn't heterosexual white male.

I don't have any earthly reason to want to infringe on anyone's free will, or their right to an individual and private vote, or their freedom to hate Hillary with every breath they draw. More power to them. Long may it wave, and vive le difference. My motives for engaging in this conversation are two: the abject fear I've mentioned, and the desire to motivate Democrats to pull together and not apart. From what I can see,Bernie and millions of Bernie followers, and Hillary and millions of Hillary followers understand that there is something bigger at stake than getting a particular Dem candidate in - that's keeping those two (I can't take Rubio seriously) OUT.

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I suspect that it is a jargon of gambling, hard to understand.

Yes, it is based on gambling. When you double down you back up your bet with an amount equal to what you originally bet. Thus you double your bet. Similarly, if a politician says something that is challenged and instead of backing off he repeats what he said and even adds to it he is said to be doubling down on his remarks.

That's unusual in AusE (or perhaps it's that I don't gamble). So when they double down on police, they're actually doubling up? Weird.

To 'double down' is a term used in blackjack which has been extended to mean doubling, [the stakes] of almost anything in any situation.

When it occurs in the quoted passage it's, 'I see a doubling down in militarized police departments…'. To answer the actual question about 'in' or 'on', I think 'in' is correct. I think it means that 'in the sphere of MPDs' a harder stance is being adopted.

Raymott said:

That's unusual in AusE (or perhaps it's that I don't gamble). So when they double down on police, they're actually doubling up? Weird.

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They're "doubling down" on the idea of more militarized police. There is not a literal doubling of forces.

Roman55 said:

When it occurs in the quoted passage it's, 'I see a doubling down in militarized police departments…'. To answer the actual question about 'in' or 'on', I think 'in' is correct. I think it means that 'in the sphere of MPDs' a harder stance is being adopted.

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If they are increasing the number of such departments, a doubling down of militarized police departments would work for me.

I would also use "double down on."

Again, it's an IDEA that you double down on.

A: I think all people who dye their hair pink or blue or other colors not found in nature are idiots!
B: That's a strong statement. Are you sure you don't want to qualify that a little.
A: NO! They are idiots, and so are those people who cut their hair in outlandish ways, like Mohawks. Idiots! All of them!

A could have backed away from his initial statement, saying something like "You're right, that's too strong. But I swear, some of these people - I don't even know where they are coming from!"

But A did NOT back away. In fact, he made an even stronger statement. He "doubled down" on his statement that people with unconventional hair are idiots.