Which occurs first: nitration or oxidation of aniline by concentrated nitric acid?
Concentrated $\ce{HNO3}$ is ‘only’ around $70~\%$. To add a nitro functionality by electrophilic aromatic substitution, typically the $\ce{NO2+}$ cation is required which is formed only by strong dehydrating agents such as sulfuric acid:

$$\ce{O2N-OH &lt;&lt;=&gt;[\ce{H2SO4}][-\ce{HSO4-}] O2N-OH2+ -&gt;[][-\ce{H2O}] O=\overset{+}{N}=O}\tag{1}$$

Concentrated nitric acid is not strong enough to dehydrate iself. Thus, nitration will typically not be observed.