I don't know where you get the confidence on Trump from, I think he's about 50/50 to win a second term.
But let's leave that alone and talk about the court as it's comprised RIGHT NOW. You have 4 near automatic votes to uphold Roe on the court. The left wing of the court is OUTCOME oriented. They want abortion to be legal, ergo they will vote to keep it legal.
That means you only need ONE conservative to flip. I can virtually guarantee that John Roberts will vote to uphold Roe. Roberts twisted himself into a legal pretzel to avoid the court doing anything controversial in the Obamacare case because he's an institutionalist. He values the institution's reputation above the rule of law, and fearing the backlash from the left over overturning ObamaCare, he blinked. He'll do it again on abortion most likely.
Further, I'm not even sure that all of the new justices would vote to overturn. Thomas would without a doubt, and has come as close as a justice can to saying as much. I think there's better than fair chances Alito would as well. But Gorsuch in particular is a bit of an iconoclast, and it would not surprise me for him to uphold it. Nor Kavenaugh. I'm not saying it's LIKELY that they would, but I wouldn't be shocked.