NEW YORK (AP) — From the biggest stage in U.S. politics, President Donald Trump made clear that on the defining issue of his presidency — immigration — he cannot or will not change his hard-line approach heading into 2020.

Yet the Republican president drew a new frame around his Democratic opposition, warning in his second State of the Union address that the rise of socialism on the left threatens the nation's core values.

Tuesday's speech was not the opening salvo of the 2020 election. That debate began almost immediately after his 2016 victory. But Trump's prime-time address offered the clea...