I’ve copied a portion of an older comment I wrote, answering part of the question:

One thing which isn’t immediately apparent, even to Americans themselves, is that the large American political parties are less equivalent to individual political parties elsewhere, and are closer to “uneasy coalitions”, like those found in Europe involving multiple parties trying (and maybe failing) to form a government. That makes it harder to draw broad conclusions like “USA Democrats would be right-of-center” because progressives and “DINOs” (Democrats in name only) within the party would be left-wing or right-wing, respectively. Logically, the same applies to the Republican party, although ranging from right-wing RINOs (Republicans in name only) and “moderate Republicans”, to the far-right factions of the party, like neo-Nazis and MAGA.

That’s what I wrote then, and what I’ll add today is that because of the enormous variety in different parts of the USA, two members of the same national political party from different parts of the country might sit down for dinner and find they have very little common group. What appeals to them about their party might be highly local.

For example, a registered Democrat in California might be fully onboard with regards to the rule of law, as applied to immigration and unlawful detention, but might be a bit apprehensive about tax reform that would eliminate middle-class subsidies (eg SALT exclusion) because that hits very hard in a HCOL state.

Meanwhile, a registered Democrat-Farmer-Labor (the state’s Democratic party) in Minnesota may be fully convinced that environmental protection is important to preserve both the planet and the nation’s public lands, but wouldn’t necessarily support the wholesale ban of hunting because of the rich cultural value instilled from an early age.

With the exception of vanguard political parties, I’m not aware of any political parties that strictly adhere to and enforce the party platform. That is to say, membership that mandates exsct alignment to the values of the party, and failure to do so requires expulsion or resignation. This is a rarity in American politics, because parties generally want the barrier to entry to be low. The downside is that there’s no party discipline whatsoever for members that aren’t in government.