I realize the bondholder representatives are saying bad things about Obama but as I understand what is going on here there is nothing unconstitutional about it.
The bondholders are being offered about what they would have gotten in a regular bankruptcy. They can take it or they can take their chances in court.
What they object to is that they aren't being given a sweetheart deal like the union pension funds are being offered. The union pension funds are probably behind the secured creditors when it comes to getting paid off in bankruptcy court. If this were a normal bankruptcy the pension fund holders would be left to try and recover something from the national pension fund insurance program. But this isn't a normal bankruptcy. The UAW is a big Democratic Party benefactor and it would be expected that the Democrats are going to give them some taxpayer money in this situation. That's just routine politics. I think it would be hard to prove that this is unconstitutional. Eight years of Bush would certainly suggest that cronyism isn't unconstitutional.
Of course, all the various GM stake holders would be much happier with the Bush administrations strategy of just throwing money at the problem. No need for any concessions, the GM stake holders just make the switch from burning through stock holder equity to burning through US taxpayer funds. No need to change anything.
And on a slightly different topic GM has sweetened the offer for bondholders:
http://tvnz.co.nz/business-news/gm-sweetens-bondholder-deal-2761936