Isn't Trump's policy towards Pakistan paradoxical, as it will expedite
a Chinese military base in Pakistan, and push Pakistan into Russian or
In Pakistan, Chinese interests (mostly in developing economic power as part of a larger "go global" policy) are not necessarily strongly at odds with U.S. interests. Both the U.S. and China are countries who are disposed to be concerned about Islamic militants and want both Afghanistan (where China (also here) and the U.S. both have some developing business interests) and Pakistan (where the same is true) to have peaceful, effective government. Moreover, the cultural and political differences between China and Pakistan are so great, that China will never be the kind of extremely tight ally that Vietnam is, for example, which is much more culturally and politically similar and economically (and geographically) tied to China, might be. Thus, the risk of Pakistan "falling into the Chinese sphere" is overstated. (The issue of Pakistan falling into the Russian sphere is trickier but also sufficiently tangential to the rest of the question that this issue is not easily integrated into the same answer.)
The U.S. also has direct military involvement in Afghanistan in which their Taliban opponents who are actively trying to kill U.S. soldiers and U.S. allies and to wrest political control from a U.S. installed civilian government in Afghanistan. These efforts are actively supported by groups in Pakistan's tribal area to which the Taliban fled when it was defeated by a U.S. led coalition in Afghanistan. Dead soldiers are a higher priority than minor diplomatic gains by a country that is neither a true friend nor a true foe (i.e. China).
So, the U.S. concern about Taliban action in Pakistan is a higher priority for the U.S. than preventing China from growing more involved in Pakistan.
As others have noted in the comments, there are also many other concerns in the U.S.-Pakistan relationship that are potentially more salient than the role of China in all of this.
N.B. Explaining the motives of the U.S. in this situation (as the question asks) is easier than explaining the motives of China, Pakistan, or Russia which all have more complex diplomatic agendas in relation to this situation that are part of global strategies, than is the agenda of the United States here, whose agenda is fairly straight forward, particularly when limited to the Trump Administration's motives in particular as in this question.