Republican Donald Trump should fix his stumbling White House campaign in the next three weeks or step down, The Wall Street Journal said on Monday in a sharply worded warning from a leading conservative voice.

Trump has alienated his party and failed to establish a competent campaign operation, the paper said in an editorial.

The Journal's editorial board, which generally favors Republicans, has been critical of Trump and has questioned his conservative credentials, but its warning on Monday was its strongest attack yet. It echoed growing alarm about Trump's candidacy among many leading Republicans who have been slow to embrace him or have completely distanced themselves.