"Poisoning the well" is getting thrown around a lot by the Republicans as a talking point but they are using it contrary to its meaning. Also why tell your opponent they are about to use a tactic that works really well in political debates and in warfare. Accusing the President of poisoning the well by issuing an executive order that would accomplish some portions of his policy preferences for long-stalled immigration reform actually would put him in an advantageous position.
I don't think they mean it the way I would mean it, as in what will happen if Keystone XL is built and it leaks into the Ogallala Aquifer, but that's another story.
Really the well the President would be poisoning by executive order would be that little puddle of potential Republican voters among Hispanics which would then shrink down to almost nothing. The President gets to take bold decisive action, a sort of political blitzkrieg on our useless Congress, and then he gets to make a fighting retreat from a divisive, complicated issue while the Republicans are forced to react and find nothing but poisoned wells of minutiae to complain about. The President ends up looking like he did big things and the Congress ends up looking small.
I used to lament that our executive branch held Congress in such disregard, but over the last 14 years, it really became clear that both Republican and Democratic administrations have been right about Congress. It is dysfunctional, gerrymandered, unrepresentative, irredeemably corrupt, and what few good people end up there have to spend more time fundraising than legislating. We'd be better off having a national popular vote President just proposing legislation through a direct democracy system.