President Donald Trump is expected to propose slashing the corporate tax rate to 15 percent on Wednesday, as the White House unveils its first stab at a tax plan, according to two sources familiar with the administration’s deliberations.Cutting the corporate rate to such a low level would allow Trump to follow through on a campaign promise that has been months in the making – even if policy experts argue that getting to that rate is impossible to do without imposing a new levy like a consumption tax, or blowing a hole in the deficit.