WASHINGTON (AP) — Worried about a potential Republican primary challenge, President Donald Trump's campaign has launched a state-by-state effort to prevent an intraparty fight that could spill over into the general-election campaign.

The nascent initiative has been an intense focus in recent weeks and includes taking steps to change state party rules, crowd out potential rivals and quell any early signs of opposition that could embarrass the president.

It is an acknowledgment that Trump, who effectively hijacked the Republican Party in 2016, hasn't completely cemented his grip on the GOP and,...