Conservative, evangelical Christianity in America is not inherently or necessarily racist. However, there has been significant convergence between racism, White Supremacy, and conservative Christianity throughout American history. Not only have conservative evangelical Christians been leading defenders of slavery, racism, and segregation, but there are aspects of evangelical doctrine which encourage the continuation of racist outcomes.
Evangelical Christianity's development as a defender of racist social structures wasn't inevitable from a theological standpoint, but it was necessary from a political one: itinerant evangelical preachers in the South made little headway so long as they retained their revolutionary attitudes. In order to become more accepted socially, they had find acceptance by society's leading figures: the white gentry. This led to numerous changes, including a new emphasis on the supremacy of whites over blacks, pushing women to the margins, acceptance of sinful behavior like drinking and gambling, and stronger defenses of social order.
Southern evangelical churches ended up on the forefront of defending slavery against Northern abolitionist movements, also generally originating in evangelical churches. Southern churches framed the defense of slavery as a religious cause and the Civil War as a Religious War. They lost, but hateful theology never dies -- it just goes underground and waits for new opportunities. In this case, the same basic theology arose again in the fight over segregation a century later.
Today few conservative evangelical Christians are openly racist, but some doctrines encourage racist outcomes. Evangelical Christianity encourages conformity and discourages efforts that "rock the boat," even if to achieve justice. Sharing the gospel takes precedence over social justice for minorities. Evangelical Christianity also generally denies the moral agency of institutions -- thus institutional racism cannot exist and so long as individuals are themselves not racist, then social outcomes must be racism-free. If it appears that blacks are failing, it must be their own fault.
A few Christians do remain openly racist, and sometimes they justify their racism or White Supremacy on the basis of Christian doctrine, just as their ancestors did. Christian racism is also not limited to conservative evangelicals. We can find it across the spectrum of Christian denominations, including Catholicism.