John R. Kasich is the former governor of Ohio, serving from 2011 to 2019. A Republican, he was previously a member of the House of Representatives. He is the author of "Two Paths: America Divided or United." The opinions expressed in this commentary are his. View more opinion articles on CNN.

(CNN) During my 18 years as a member of Congress -- not so long ago -- my colleagues and I didn't robotically toe the line with the President. Republicans didn't vote in lockstep with Republican presidents, not even Ronald Reagan. And Democrats departed from their party's president when they thought it was the right thing to do. We took party loyalty seriously, but we gave even greater weight to principle.

Gov John Kasich 07162018

In recent decades, of course, partisanship in the House and Senate has become far more intense, and the nation is worse as a result. But even now, in this hyper-partisan era, there comes a time when our elected leaders must put country over party.

One such moment: the ongoing debate over President Donald Trump's national emergency declaration to fund construction of a wall on the US-Mexico border. Sometime soon, Republican senators will have the opportunity to demonstrate -- as 13 Republicans did in the House -- their love of country and their commitment to constitutional values by voting for the resolution to disapprove the President's emergency declaration. Instead of acting like they're afraid of their own shadows, Senate Republicans must use this vote to -- at long last -- stand up and defend the Constitution.

Let's be clear. This vote is not about the situation at the border; it's about an executive power grab and, above all, congressional respect for the democratic process. Whatever their views on the border situation -- which I agree is serious -- Republicans should oppose the President's declaration. Standing against the President on this issue is important not just for today, but for our future.

For years, Republicans decried executive overreach by President Barack Obama. If we are serious about our constitutional values, we can't complain only about actions by the other party. We have to apply consistent principles whenever we have a president from our own party as well.

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