Supreme Court nominations are not always cakewalks, however, as cases such as Harriet Miers and Robert Bork (and Clarence Thomas) attest. There are several potential risks to Trump and Republicans:
Trump could nominate a relatively moderate justice, in an effort to keep Collins and Alaska’s Lisa Murkowski on board and to put maximum pressure on red-state Democrats, but then face a backlash from conservatives.
Trump could nominate someone very conservative, but at the price of actually putting votes such as Collins’s and Murkowski’s at risk and of turning off swing voters.
Trump could nominate someone who had vetting issues, or someone who triggered a debate about qualifications, or someone who was seen as too much of a political crony. Historically, these sorts of justices have had trouble getting confirmed.