Critics From Across the Spectrum Rip Plan

WASHINGTON—A barrage of instant criticism blasting President Barack Obama's new Afghanistan strategy from across the political spectrum signaled the challenges ahead in selling the plan to a skeptical public and Congress.

Some of Mr. Obama's most loyal supporters among liberal grass-roots groups denounced the 30,000-troop escalation—despite a newly revealed plan for a quick drawdown that White House officials had hoped would mollify the left.

Many Republicans, while supporting the troop increase, were quick to charge that the timetable for withdrawal would embolden U.S. adversaries. Arizona Sen. John McCain warned that Mr. Obama risked telling the enemy "that you're coming and you're leaving."

Mr. Obama's nationally televised address Tuesday kicked off a full-blown campaign by the White House to rally support for a troop escalation that could bring rising U.S. casualties just as lawmakers are running for re-election next year.

The plan appears designed to minimize political fallout—calling for a progress assessment a month after the November 2010 congressional elections and initiating the troop exit the following year as Mr. Obama begins ramping up his own re-election campaign.