As I’ve argued here, the political battle over the current migrant border crisis is in many ways a warm-up for the bigger battle to come, over Obama’s coming executive actions to ease deportations. Republicans are seizing on images of kids crossing into South Texas to hype a general sense of a border in chaos and associate that imagery with Obama permissiveness and weakness on immigration policy in general — with the goal of constraining his sense of space to act alone deportations.

But how far can Obama go legally? Politico has a good piece spelling out the dimensions of the legal debate. No matter how far he goes, it’s unlikely Republicans can sue over it, Politico notes, but some experts think he’s got a lot of leeway:

“There is, I think, a general consensus that his authority to take executive action is fairly wide as long as it is based on executive branch authority to use prosecutorial discretion to decide how people are treated who are subject to deportation,” said Doris Meissner, Immigration and Naturalization Service Commissioner under President Bill Clinton.

“He’s got a continuum of options from a fairly narrow reworking of deportation priorities all the way to a new program of some kind that would allow more numbers of people to apply for work permits of some kind,” she added.

What Obama has done so far on immigration and what he’s likely to do in the future can be justified on the theory of prosecutorial discretion, the long-standing executive branch power to decide in which cases the law should be enforced, [University of California professor Hiroshi] Motomura said.

“We have a system that runs on discretion. There are 11 million people in the country who in theory are not supposed to be here. Congress has funded the capability to deport maybe half a million people a year,” the professor said.

This last point may be crucial, because the Obama administration is probably on more solid legal ground defending whatever action he takes as an exercise of discretion over the prioritization of enforcement resources. Foes will argue that Obama’s action amounts to wholesale policy-making over a large class of people, which some experts believe crosses a legal line. But until we see what Obama proposes, and the administration’s legal justification for it, it’s impossible to know how the legal argument will play out.

The politics of this are unclear and probably volatile. While the public broadly supports legalization of undocumented immigrants under certain conditions, it’s unclear what sort of impact it will have when Obama acts unilaterally to protect some of them, particularly since Republicans are planning to make #ObummerLawlessness central keeping the base in a frenzy through Election Day. On the other hand, there’s serious long term risk for Republicans here: The anger of conservatives will require a scorched earth response from GOP lawmakers, which risks overreaching and energizing the Dem base, even as Republicans will be boxed into a place where they are continually upping their demands for more and more deportations — with untold long term ramifications among Latinos.

I tend to doubt that Obama’s move will be as ambitious as even some of the reports are indicating. But in the end, I hope the administration makes its decision based solely on what it genuinely determines is legally, rather than politically, possible. And by the way, that could end up constraining whatever Obama does as easily as it could end up leading him to do something very ambitious, depending on what administration lawyers determine.

* DEAD HEAT IN KENTUCKY? A new Bluegrass poll finds Mitch McConnell leading Alison Lundergan Grimes by two points, 47-45. This poll is of likely voters, which means it reflects the midterm voter dropoff Dems are likely to face — yet Grimes is within the margin of error.

Still, the polling average now has McConnell up three points, which is not insignificant. The Grimes camp notes they have maintained a near tie after facing millions in outside attack ads, and say they are poised to begin seriously spending the cash she’s stockpiled.

* WHITE HOUSE PRESSES ECONOMIC CASE ON CLIMATE CHANGE: Today the White House will release a new report claiming that failure to reduce carbon emissions could cost the economy $150 billion a year. With Republicans bashing red state Democrats over the economic costs of Obama’s plan to curb carbon emissions, this report is part of a broader effort by Dems to shift the debate by making an economic case for acting on climate.

As Robert Rubin puts it, “much of the debate about climate change…is framed as a trade-off between environmental protection and economic prosperity…that’s precisely the wrong way to look at it. The real question should be: What is the cost of inaction?”

* ACTING ON CLIMATE IS FISCALLY RESPONSIBLE: The New York Times adds that Democrats are also ramping up the case that failure to act poses a long term threat to the federal budget, due to record expenditures on droughts, wildfires and floods:

Democrats hope that argument will win over some fiscally conservative Republicans. Most Republicans have said that the E.P.A. climate-change rules exemplify what they call the Obama administration’s overreach.

So “fiscally conservative Republicans,” who are often only fiscally conservative when it comes to spending they don’t like, will suddenly prioritize their “fiscal conservatism” over their hatred of #ObummerLawlessness? Yeah, that’ll happen.

* DEMS PREPARE BORDER VOTE: Senate Democrats will probably vote tomorrow on their own proposal to provide $2.7 billion in funding to address the border crisis, with no changes to the 2008 law attached. Republicans will likely oppose it because it doesn’t change the law to expedite deportations.

Meanwhile, House Republicans may not be able to pass their own border proposal, because its measures to expedite deportations could drive away the Dems they will need to pass something, given conservative opposition. Anyone else noticing a pattern in the GOP position here?

* MARRIAGE EQUALITY KEEPS ON MOVING FORWARD: A federal appeals court in Virginia has struck down the state’s gay marriage ban, another in a remarkable string of victories for gay civil rights, and crucially, this latest decision declares the ban an unconstitutional form of “segregation.” Robert Barnes and Jenna Portnoy observe: “Two federal appeals courts have now said the bans are unconstitutional.”

All of which again suggests that the issue could soon find its way back to the Supreme Court, which may declare a Constitutionally protected right to gay marriage.

* KAY HAGAN PUSHES ‘MODERATE’ CREDENTIALS: Embattled North Carolina Dem Senator Kay Hagan is up with a new ad touting her credentials as a moderate: “Republican or Democrat — if an idea works for middle class families, I am all for it,” Hagan says. “Not too far left. Not too far right. Just like North Carolina.”

This appears intended as pushback against the relentless barrage of spending tying Hagan to Obama, as well as to lay the groundwork to make the case that foe Thom Tillis has presided over a legislature that has lurched the state sharply to the right.

* AND THE ANTI-OBAMACARE LAWSUIT IS BOGUS: Jonathan Cohn turns up email evidence that undercuts the case that Congress intended the Affordable Care Act to deny subsidies to those on the federal exchange, to induce states to set up their own — which could severely damage Obamacare if SCOTUS upholds it. The email

is consistent with a ton of circumstantial evidencelike the assessments from the Congressional Budget Office and Joint Tax Committee, as well as the wording of the rest of the bill, all of which suggest lawmakers intended for subsidies to be available everywhere…It’s a window into what the legislation’s authors were thinking at the time that they wrote it. And their opinion is the only one that really matters.

Well, one hopes their opinion is the one that matters, anyway! Also don’t miss Brian Beutler’s takedown of the Halbig Truthers.

What else?

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.