Federal Government/Federal Power
For many on the left, the federal government is a (cautiously) trusted entity crucial to the well-being of Americans on many levels. From this perspective, the federal government deserves to have the power it needs to govern effectively and do the right thing. For instance, if reducing carbon emissions is essential to the well-being of the planet, then the federal government needs the regulatory authority to regulate emissions in every state.
For many on both the right and the left, the federal government has come to be seen as a large, bloated entity that has long exceeded its appropriate constitutional role - e.g. regulate commerce with foreign nations and between States, immigration, coin money, declare war, raise an army, etc. Compared to this relatively small set of functions, conservatives see the federal government in its current stature and scope as leading to waste and illegitimate coercion that harms the economy and interferes with local communities.
Indeed, most on the right see the gradual growth in the power of the federal government (apart from the military), and consequent reduction in the power of the states, as a violation of both the letter and spirit of the US Constitution. Many on the left also decry the ever-increasing size and power of the federal government (including the military), seeing in it one half of a dangerously anti-democratic crony capitalist collusion with Big Business. The libertarian right is particularly outraged by a long string of Supreme Court decisions throughout the 20th century which centralized power. For instance, in Wickard v. Filburn (1942) the court decided that a farmer growing wheat on his own land for his own consumption constituted “interstate commerce” on the grounds that he thereby reduced the demand for wheat nationally. The right regards this as an illegitimate expansion of federal power.
Issues such as marijuana legalization create strange bedfellows with respect to federalism. Many progressives join with libertarians in supporting the right of states to craft their own policies. Meanwhile conservatives often want to use the authority of the federal government to shut down state-level marijuana initiatives.