Flash.....news to the Trumpsters....he lost. It's none of Texas's business how Pennsylvania (or any other state) conducts their elections. Just it's none of the business of Pennsylvania how Texas conducts their elections.
Totally wrong, of course.
The Constitution requires the state LEGISLATURES to determine how their state selected presidential electors.
No the executive branch via edicts from the Secretary of State.
Not the judicial branch via court rulings changing procedures, such as how late magic mail-in ballots can be recieved, etc.
The state LEGISLATURE decides.
ONLY the state legislature.
When the executive and judicial branches of half a dozen states arbitrarily and unconstitutionally decide to set aside the laws of the legislature and thus invalidate a critical element of the selection of the President, those goons are effectively and in actuality disenfranchising the voters of the 75 million Americans that voted for the real president and, if the laws had been been followed, elected President Trump by an electoral landslide.
To protect the rights of their citizens, Texas and the dozen or so other states that joined the lawsuit most eminently had standing to sue. Because....
...it was NOT the "state of Pennsylvania" that violated the Constitution, it was the unlawful goons overstepping their utter lack of authority to have any input at all.
And the Supreme Court failed completely to perform it's task of protecting the rights of the people.
Article 2, Section 1, Clause 2
Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors, equal to the whole Number of Senators and Representatives to which the State may be entitled in the Congress: but no Senator or Representative, or Person holding an Office of Trust or Profit under the United States, shall be appointed an Elector.