No one doubt that the push to overhaul the nation’s immigration system is imperiled by hard-liners who would gut reform legislation by removing any realistic prospect of citizenship for undocumented residents. With anti-reform forces preparing their assault, it’s critical that the pro-reform camp doesn’t provide them with ammunition.

President Obama last week cautioned advocates not to allow their hopes for a perfect bill to subvert a good one that satisfies a set of basic criteria. For the president, those criteria included continuing to tighten border security, cracking down on unscrupulous employers, streamlining and rationalizing the unwieldy immigration bureaucracy and providing a route to citizenship — even if it takes more than a decade.

Whether pro-immigrant groups heed the president’s advice may determine the outcome of the coming debate in Congress. It’s not clear they will.

Vowing to press hard for “improvements,” groups say they will try to strip provisions in the Senate bill forged by the bipartisan Gang of Eight that could prove onerous for some immigrants seeking legal status and citizenship. Those include provisions requiring that immigrants provide rigorous proof of ongoing employment, show almost unblemished criminal records and pay $2,000 in penalties and fees over 10 years, even before they are allowed to apply for citizenship (which itself involves $680 in fees, plus possible legal costs).

Some reform advocates will insist on retaining visa preferences, stripped under the current legislation, for siblings and married grown children of U.S. citizens. Some will object that the bill eliminates the so-called visa lottery, under which tens of thousands of Africans and East Europeans immigrate to the United States annually. Civil rights groups, in particular, will insist on amending the bill to provide visas for the foreign same-sex spouses of American citizens.

Many pro-reform groups also object to the Senate bill’s arbitrary cutoff date, which would allow only immigrants who arrived before 2012 to apply for legalization. That would mean those who arrived more recently — perhaps a couple of hundred thousand — would remain hidden and off the books, probably for many years.

A reasonable case can be made for all of these points. But festooning the Senate bill with provisions pleasing to reform advocates would make it a fatter target for conservatives who want it to fail.

Why provide anti-reform lawmakers with fresh arguments and and angles of attack? Better to make them rehash their stale old playbook. They will cry “amnesty.” They’ll argue that reforms should be piecemeal, leaving citizenship for another day (i.e. never). They’ll insist on an unattainable metrics of border security.

Americans have grown tired of such pretexts. In polls, they overwhelmingly favor legalization and a path to citizenship. That, and Republican alarm at losing the Latino vote, have generated fresh momentum to fix the nation’s broken immigration system. Those who favor a fix should be wary of asking too much and, in the process, sapping that momentum.