WASHINGTON—Many Republican lawmakers lie low when they have differences with President Trump. Sen. Rand Paul has taken the opposite approach.“Congress needs to grow a spine, and Congress needs to stand up for its prerogatives,” the Kentucky Republican told reporters, complaining that Trump relied on a national-emergency law to impose tariffs that Paul believes should be controlled by lawmakers. His comments came just days after he was one of only two GOP senators to vote against the party’s budget framework that is key to Trump’s tax cuts, saying it didn’t do enough to reduce the deficit.