Actually, the 270 is established by LAW (12th Amendment). 270 = all states 50+Dc = 2 senators + Rep from each state. Do the math, 538 electoral votes. Majority = 270.
No again, if Trump only has 266 EV and Clinton has 232 EV, then it goes to the House per the 12th Amendment.
The person having the greatest Number of votes for President, shall be the President, if such number be a majority of the whole number of Electors appointed; and if no person have such majority, then from the persons having the highest numbers not exceeding three on the list of those voted for as President..."
The key is "electors appointed". If electors from those three states are not appointed due to recounts, they do not count at all.