What are three distinct national-level “party planks” for the RNC and the DNC?

The three distinct national-level "party planks" for the RNC and the DNC are American's liberalism, conservatism and individual support towards policies.

Explanation:

"Plank" is the term often given to the components of the political platform the opinions and viewpoints about individual topics, as held by a party, person, or organization. A party platform is sometimes referred to as a manifesto or a political platform.

The platform of the Republican Party of the United States is generally based on American conservatism, in contrast to the modern liberalism of the Democrats. ... In foreign policy, Republicans favor increased military spending and unilateral action.

The platform of the Democratic Party of the United States is generally based on American liberalism and American progressivism, in contrast to the conservatism of the Republican Party. ... Democrats tend to agree with the scientific consensus on climate change, and support clean energy and cap-and-trade policies.