I am a little bit lost at this apparent "academic consensus of power hierarchy defining for racism" in relation to the term, because I have studied social sciences academically and this is absolutely not how it was explicitly defined. Definition of the term is an argument within itself, absolutely, but there is no "consensus" that I have been exposed to, though some social scientists will argue that the hierarchy is a necessity (eg: you cannot be "racist" against the ethnic group with power). Hierarchy is mostly discussed as a necessity for racism to exist, as in racism requires there to be a social hierarchy based on race, as race is a social construct. This obviously weights ideological racism towards the oppressed end of the hierarchy from the top, but they're not mutually exclusive. And in my opinion the belief that racism requires an inherent, already existing power imbalance, does a tremendous disservice to, dangerously so, the exploration and understanding of development of racist ideologies and belief systems within individuals and groups that can, if left unaddressed, propagate and develop into systemic racism via a power hierarchy.
Race is a social construct, that is an academic consensus, though we use "racism" to also include ethnic groups as well. Interchanging acts of racism with "prejudice" makes no rational sense, as it does not identify the very specific ideological context of racial superiority. "Prejudice" is an extremely broad identification of irrational belief resulting in divisiveness, and not required to be fuelled by racial or ethnic beliefs. It implies that racism as a concept cannot exist without a strict and existing power imbalance between ethnic groups, and is a term only subjected to by the lower hierarchical from the upper hierarchical within a society wherein that power imbalance exists. It prevents us from identify the unique and dangerous facets of specific racial supremacy ideology within individuals and smaller ethnic groups that can lead to power imbalances, and create and enforce exactly this racially divisive hierarchy. It also closes us off to understanding the development of racist beliefs within existing ethnic groups, and how violent acts of oppression stemming from adherence to ideological racism are often acted before an enormous power imbalance is developed, and in historically poignant examples were the very fuel of developing a power imbalance.
I understand the context within the United States is especially unique and complex, because of its history and undeniable, factual institutionalised racism and oppression that exists within a white, anglo dominant social hierarchy to the detriment of...well, everybody else. Australia has very similar issues, and as a white man living in this country I'm very well aware of our own systemic racism. But when we discuss racism we are not just talking about just the West, nor ethnic divides caused by racial supremacy where "white people" sit at the top. If people wish to have that discussion, particularly within the social framework of the United States, that would make for a very interesting topic. Some of the answers here are more appropriate if the question is framed "Is it possible to be racist to a degree of significant towards Whites in the United States of America?". Exploring how racism manifests within societies, ideologically within ethnic groups, and is then enforced as a means of oppression is an incredibly fascinating topic. But manifestations of racism as an ideology within ethnic groups and how they develop over time is sadly not unique to Western civilisation, nor the most globally dominant form of racial supremacy (aka, "Whites").
And I simply don't think it's intellectually just to prop up the systemic, institutionalised racism of the United States, or even racism as a consequence of global colonialism (which is really the root of all white supremacy driven racial divides), as exclusively the definition of racism in the face of monstrous historic tragedies of ethnic and racial cleansing, either removed from white culture (the Rwandan genocide), or within it (the entirety of World War II, from multiple belligerents).
This is, of course, all matter of debate and discussion. Social science is incredibly interesting in how we explore social stratification, particularly in relation to race (which, again, is a social construct and arguably doesn't even "exist"), alongside ethnic groups, the various institutionalised oppression that have formed at various levels within societies. Human beings are unfortunately pretty fucking horrible when committed to and driven by ethnic/racial ideological divide.