AMES, Iowa — Tim Pawlenty was first in line to enter the Republican presidential race. He is now fighting to avoid becoming the earliest major candidate to be shown the door.

No contender for the Republican nomination has followed the conventional playbook more than Mr. Pawlenty, a former governor of Minnesota who began introducing himself two years ago during a prospecting trip to Iowa. Yet his path has been complicated by fresher faces, an unruly nominating contest and a handful of missteps that swallowed his summer momentum.

The voting will not open for at least six months, but Mr. Pawlenty knows that his performance at the Iowa Straw Poll on Aug. 13 — fair or not — will help determine whether his candidacy accelerates or lands in the annals of Republican presidential hopefuls like Elizabeth Dole, Lamar Alexander and Dan Quayle whose campaigns were extinguished here.

The sense of urgency was apparent as Mr. Pawlenty made the case to Republicans that an experienced candidate was preferable to an intriguing one. If Michele Bachmann, his fellow Minnesotan, was on his mind, he did not say so directly, but there was little mistaking his point.