What standing does one state have to determine if another state(s)' implementation of their own constitution violates the federal constitution?

Question

Background

Various media outlets have been reporting on the notoriety and expansiveness of State of Texas vs. Commonwealth of Pennsylvania, etc.. This lawsuit alleges the following:

• Non-legislative actors’ purported amendments to States’ duly enacted election laws, in violation of the Electors Clause’s vesting State legislatures with plenary authority regarding the appointment of presidential electors.

• Intrastate differences in the treatment of voters, with more favorable allotted to voters – whether lawful or unlawful – in areas administered by local government under Democrat control and with populations with higher ratios of Democrat voters than other areas of Defendant States.

• The appearance of voting irregularities in the Defendant States that would be consistent with the unconstitutional relaxation of ballot-integrity protections in those States' election laws

Issue

While the Supreme Court does have original jurisdiction over suits between two or more states, this suit seems to state that the way other states allegedly failed to follow their own state law in turn led to these states not following federal law. There do exist cases where the Supreme Court invalidates certain state laws, but I do not see a successful case where a state invalidates another state's law on the basis of the other state's law violating the U.S. constitution. Rather the cases I cited with two or more states seem to be with contractual disputes as opposed to one state saying that another state's law is wrong. This leads me to question...

Question

Can one state appeal a suit to the supreme court about the validity of a different states' state law in relation to the federal constitution?

Answer 1

The direct answer is "no" and the indirect answer is "yes", that is, your way of putting the matter diverges significantly from how the Bill of Complain puts the matter. The claim is that the defendant states violated the Electors Clause, the Equal Protection Clause, and the Due Process Clause. Texas claims that there is an injury in fact, citing various SCOTUS rulings e.g. Wesberry v. Sanders which says that

No right is more precious in a free country than that of having a voice in the election of those who make the laws under which, as good citizens, we must live. Other rights, even the most basic, are illusory if the right to vote is undermined

See the argument in the brief for more legal rhetoric. There can be no question that one state can sue another; equally clearly, the plaintiff must show actual harm and not just annoyance. New Jersey v. New York is a case involving a question of equity, not the federal constitution, but there is no legal principle to the effect that one state cannot sue over a constitutional harm rather than an equitable harm. See the brief p. 65 ff. The court does not require that there be exact precedential analogs (otherwise, Roe v. Wade would have turned out differently), what's required is simply that there be reasonable logical steps: SCOTUS gets to decide what is reasonable (or it can decline to decide).

Answer 2

Can one state appeal a suit to the supreme court about the validity of a different states' state law in relation to the federal constitution?

Yes, at least to the extent that state legislature ought not to circumvent U.S. constitutional constraints with which all other states have to comply, since that circumvention might put compliant states at an unfair disadvantage.

For instance, in the context of presidential elections, a state's legislature might translate to an unconstitutional work-around or circumvention of the apportionment of electors. Hence, any state has a legitimate interest to preclude other states' legislature or conduct from diluting that state's electoral "weight".