Sorry, my phrasing of "not how it works" is more about willingness from the lender side and not "allowed" to. He couldn't even get a bond for for the reduced amount without going through a shady company. He's certainly not going to get 4 bonds.

use two or three surety companies, each taking, let’s say, a $50 or $75 million piece to total up to $175 million.

Even with split up bonds to reduce risk in a normal situation, the bonding company is going to assess risk based on the full cost of the bond. They personally only have to put up less money, so the "how much do i lose if everything goes wrong" scenario is less, but "how likely is it something goes wrong" involves "the person on trial for lying about finances doesn't actually have enough to cover the full bond, so perhaps that increases the odds of me getting my money back"

Why would you throw away $50 million dollars. It's "less risk" only because it's less money. But if you think he's shady enough that likely you never see the money again, then why put up any money, especially if you have to compete with others to get the payout.

If someone said "You can gamble $50 million or $400 million. If you win you get 5%, but the odds of winning are only 10%, and if you lose you only get back $10 million." You would obviously opt to gamble the $50 million. You want to lose less money. The payout isn't worth it given the odds. If you were then told "oh, you can just opt out and avoid the dumpster fire of a deal", you are going to choose to opt out. No amount of "it's less risk" will make this a good deal for a bonding company.

So yes, syndicating the bond is an option, no smart bonding company is going to touch this, which means even with syndicating it will be hard for him to find enough incompetent, shady, unlicensed bonding companies.

And to be clear, this is not me arguing in favor of why any amount of money was unfair to expect Trump to acquire. This is me pointing out why he's never going to get the money from legit sources because he's a financial dumpster fire, and they should just throw the book at him instead of continuously going easy on him.

edit:

But with Donald Trump bragging that he has $500 million cash in the bank, combined with the other assets we know he has in real estate

Trump bragging about made up numbers don't make anyone more confident about his assets. Both the value of his assets and how much stake in those assets is actually his is a thing he notoriously lies about. He's even been found guilty about lying about his finances I think.

If he actually had that money money just in the bank, none of this would be an issue, but the thing is... it's not true.