Conservatives want to increase the power of those government institutions that are the least accountable, and are most connected to the use of violence: the police and the military. They want to reduce the power of any government institutions that would serve to provide public accountability to other power centers in US society, mainly corporations and the wealthy. Corporations and the wealthy need police: to protect their property, to enforce property relations and quell unrest. They need the military: to ensure them access to foreign resources and foreign markets. They're also willing to take advantage of any other government expenditures that benefit them (infrastructure), but generally want to see any expenditures be under their control if not eliminated.
The Left ultimately wants to abolish government power and create a stateless, classless society. Leftists differ among themselves with regard to the value of government power in achieving this, with the two opposite poles of the discussion being anarchists and Marxist-Leninists. But in general, leftists realize that they have nowhere near the organizational power to even think about those goals, and just want to improve the material conditions of working-class people, who make up the majority of society.
The Democratic Party is far from being controlled by leftists: I can count the number of actual leftists in the US House on one hand, and in the Senate on one finger. The Democratic Party is a center-right party, dedicated above all to the stability of the existing ruling class. They sometimes virtue-signal cultural values that are shared with the left (feminism, anti-racism), but largely as a means of providing an outlet for those values that is not threatening to capitalism, and which can be co-opted to protect it.