In stunning news this morning, President Obama has reversed course and will propose a kind of Glass-Steagall II, as well as some kind of provision to rein in too-big-to-fail banks.

Make no mistake about, this is a massive story. You’d think The Wall Street Journal would have it splashed across its front page, but you’d be wrong. Hard to figure this news judgment: It goes with this tepid news story instead: “China Seeks To Temper Boom, Stirs Growth Fears,” dropping the Obama news on A2. The lede has top editors’ (Murdoch lieutenants) fingerprints all over it, calling the move “the administration’s latest assault on Wall Street.” “Latest assault?” When would the first one have been?

That said, its story is pretty solid from there on down. It, Bloomberg, and the Times point out that this is a victory for Paul Volcker, the up-to-now-ignored former Fed chief and current Obama adviser.

Mr. Obama’s proposal is expected to include new scale restrictions on the size of the country’s largest financial institutions. The goal would be to deter banks from becoming so large they put the broader economy at risk and to also prevent banks from becoming so large they distort normal competitive forces. It couldn’t be learned what precise limits the White House will endorse, or whether Mr. Obama will spell out the exact limits on Thursday.

Mr. Obama is also expected to endorse, for the first time publicly, measures pushed by former Federal Reserve Chairman Paul Volcker, which would place restrictions on the proprietary trading done by commercial banks, essentially limiting the way banks bet with their own capital. Administration officials say they want to place “firewalls” between different divisions of financial companies to ensure banks don’t indirectly subsidize “speculative” trading through other subsidiaries that hold federally insured deposits.

Nobody gets the details on what exactly the size restrictions would be or how they would be enforced. It’s unknown if the White House will set asset-size caps on banks (unlikely) or structure disincentives like taxes and fees that grow as banks get bigger. Until we know this stuff it’s going to be difficult to say for sure just how tough this is.

But no doubt about it, this is a major switcheroo by the administration and a throwing down of the gauntlet at Wall Street, which has so far shown the ability to block or water down any real change it doesn’t like—with the aquiescence of Obama and Co.

The lobbying battles to come over this will make the skirmishes we’ve seen so far look petty. The press will have to keep a close eye on the behind-the-scenes wrangling, the money floating into PACs and congressional campaign coffers, as well as analyzing the implications of the moves for the banks and for the economy (and the political implications for an administration that’s in trouble in no small part because of its lack of forcefulness with Wall Street).

For now, it’s a break in the clouds. This is something Wall Street really does not want.

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Ryan Chittum is a former Wall Street Journal reporter, and deputy editor of The Audit, CJR's business section. If you see notable business journalism, give him a heads-up at rc2538@columbia.edu. Follow him on Twitter at @ryanchittum.