ALEDO, Tex. — In an unmarked office building in this ranching town, among thousands of Revolution-era documents and two muskets with bayonets, David Barton might seem like a quirky history buff. But the true ambition of this slender man in cowboy boots is to use America’s past to remake its future, and he has the ear of several would-be presidents.

Mr. Barton is a self-taught historian who is described by several conservative presidential aspirants as a valued adviser and a source of historical and biblical justification for their policies. He is so popular that evangelical pastors travel across states to hear his rapid-fire presentations on how the United States was founded as a Christian nation and is on the road to ruin, thanks to secularists and the Supreme Court, or on the lost political power of the clergy.

Through two decades of prolific, if disputed, research and some 400 speeches a year on what he calls the forgotten Christian roots of America, Mr. Barton, 57, a former school principal and an ordained minister, has steadily built a reputation as a guiding spirit of the religious right. Keeping an exhaustive schedule, he is also immersed in the nuts and bolts of politics and maintains a network of 700 anti-abortion state legislators.

Many historians call his research flawed, but Mr. Barton’s influence appears to be greater than ever. Liberal organizations are raising the alarm over what they say are Mr. Barton’s dangerous distortions, including his claim that the nation’s founders never intended a high wall between church and state.