NEW YORK, Sept 9 (Reuters Breakingviews) - Subprime is the crisis that keeps on giving. Mortgages made to mostly American borrowers with questionable credit histories helped sink well-established financial firms like Lehman Brothers, Merrill Lynch and Countrywide some three years ago. They're now threatening the viability of the survivors, like Merrill and Countrywide's new owner Bank of America, with their second wind in the courts.

Unpacking the lawsuits can be as confusing as the subprime securities themselves. The legal entanglements not only involve countless plaintiffs, defendants, jurisdictions and prosecutors, but they envelope each link of the modern mortgage-lending chain. The Federal Housing Finance Agency suit filed last week against 17 banks is just the latest in a long line of high-profile cases that have hammered bank stocks.

Herewith, Breakingviews offers a cheat sheet of sorts on four of the biggest cases that investors in the financial industry will need to watch:

1) Foreclosuregate - Attorneys general from the 50 states want mortgage servicers like Bank of America, JPMorgan Chase and Wells Fargo to pay upward of $20 billion among them for incompetence, or worse, in the banks' back offices. The case is rooted in accusations that banks may have wrongly foreclosed on homeowners without adequately completing and reviewing pertinent paper work. The banks would like any settlement to go well beyond so-called robo-signing. They'd like a broader release from potential liability in other parts of the mortgage-lending chain, like securitization. If BofA, JPMorgan, Wells, Citigroup and others can prevail, they would cut off at least one tentacle choking bank stocks. If they don't, expect attorneys general from a host of states to zero in on the now-idled securitization business -- the subject of the other three lawsuits of consequence.

2) The FHFA hunt - The nearly $200 billion of suspect mortgage-backed securities certainly caught investors' eyes when Fannie Mae and Freddie Mac's regulator filed its lawsuit against 17 financial institutions. But how much the FHFA actually suffered in losses -- and will request in damages -- is still unclear. The FHFA says the banks, which include BofA, JPMorgan and RBS, allegedly misrepresented facts about the mortgage bonds they sold to Fannie and Freddie. The fear is the payout could be potentially huge, roughly $39 billion, if the FHFA's earlier suit against UBS is anything to go by; anything smaller than that could lift investor spirits. Separately, Fannie and Freddie are the subject of a Securities and Exchange Commission probe into whether they disclosed the true risk of their exposure to risky home loans. The New York Times reported late on Thursday that a settlement, which would entail no admission of wrongdoing or fines, is expected soon.

3) An insurer's wrath - AIG has its sights on BofA. The insurer, whose own collapse in 2008 led to a $180 billion-plus government bailout, claims that it was defrauded in connection with the mortgage bonds it bought. After talks with the bank stumbled earlier this year, AIG decided to sue for $10.5 billion. AIG, like Fannie and Freddie, was hardly a novice investor, but if the insurer proves the banks lied about what was being sold, as AIG alleges, the level of its expertise in mortgage investing shouldn't matter. AIG is also considering litigation against other financial institutions that may have misrepresented the risk of the mortgage bonds they sold.

4) The not-so-done deal - BofA looked like it had one big suit sewn up. In June, it reached a tentative $8.5 billion settlement with institutional investors, including PIMCO, BlackRock and the Federal Reserve, on home loans that violated representations and warranties about a borrowers' creditworthiness. Such breaches can lead to banks being forced to buy loans back from investors. The wide-ranging deal would have gone a long way to putting such claims to rest. But some investors are contesting the settlement, and New York State Attorney General Eric Schneiderman is investigating whether the deal shortchanges investors.

The good news is that settlements in these cases would at least give shareholders something to work with when trying to figure out just how much an individual bank stands to lose. But more lawsuits could be in the works. With roughly $1.1 trillion of risky mortgage bonds still outstanding, there are sure to be plenty of disgruntled investors contemplating whether they should take their complaints to the courts. Shareholders will have to decide whether the legal limbo is worth the risk.

CONTEXT NEWS

-- The Federal Housing Finance Agency said on Sept. 2 that it is suing 17 banks, including Bank of America, JPMorgan and RBS for allegedly misrepresenting mortgage bonds they sold to Fannie Mae and Freddie Mac, the housing agencies taken over by the government in 2008. The par amount of the securities affected is nearly $200 billion. The FHFA has not estimated how much it hopes to recover from the banks. Separately, Fannie and Freddie could be close to a settlement with the Securities and Exchange Commission concerning their disclosure of risky mortgage loans.

(By Agnes T. Crane and Reynolds Holding, Reuters Breakingviews columnists. The opinions expressed are their own.)

Follow us on Twitter: @ReutersLegal